MODULE 1 INTRODUCTION My Training Period: hours Notes: You can remove the system("pause"); and its stdlib.h header file (if applicable) in the program examples. This code just to capture the console output for Borland C++ that was run through IDE. For Microsoft Visual C++/.Net, Borland Turbo or running the program using Borland command line, gcc etc. no need to include this code. For other compilers, please check their documentations.Abilities

Able to understand the brief history of the C/C++ language. Able to understand the C/C++ advantageous. Able to understand the basic program development cycle. Able to understand the basic structure of C/C++ program. Able to be familiar with writing codes, compiling and running a program. Able to recognize a portable main() function. Able to recognize the C and C++ standards: ANSI C/C++, ISO/IEC C/C++, POSIX and Single Unix specification.

1.1 Brief History

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C evolved from two previous languages, BCPL (Basic Combined Programming Language) and B. BCPL was developed in 1967 by Martin Richards as a language for writing operating systems software and compilers. Ken Thompson modeled many features in his language, B, after their counterparts in BCPL and used B to create early versions of UNIX operating system at bell Laboratories in 1970 on a DEC PDP-7 computer. Both BCPL and B were typeless languages, that means the only data type is machine word and access to other kinds of objects is by special operators or function calls. In C, the fundamental data type includes characters, integers of several sizes and floating point numbers. The derived data types were created with pointers, arrays, structures, unions, functions and classes. The C language was evolved from B by Dennis Ritchie at Bell Laboratories and was originally implemented on a DEC PDP-11 computer in 1972. It was named C for new language. Initially, C used widely as the development language of the UNIX. Today, virtually all new major OS are written in C. C is hardware independent, so it is portable to most computers without or with little code modification. The rapid expansion of C over various types of computers led to many variations. These are similar but incompatible. So, a standard version of C was needed. In 1983, the X3J11 technical committee was created under the American National Standards Institute (ANSI) Committee on Computer and Information Processing (X3) to provide an ambiguous and machine-independent definition of the language and approved in 1989, called ANSI C. The document is referred to as ANSI/ISO 9899:1990. The second edition of Kernighan and Ritchie, published in 1988, reflects this version called ANSI C, then used worldwide. The more general ANSI then adopted by ISO/IEC, known as ISO/IEC C. Because C is a hardware-independent, applications written in C can be run with little or no modifications on a wide range of different computer systems.

1.2 Advantageous

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Powerful and flexible language - What can be achieved is only limited by your imagination. It is used for Operating System, compilers, parsers, interpreters, word processors, search engine and graphic programs. Portable programming language - C program written for one computer system (an IBM PC, for example) can be compiled and run on another system (a DEC VAX System perhaps with little or no modification). Is a language of less keyword - Handful of terms called keywords in which the languages functionality is built. A lot of keywords doesnt mean more powerful than C.Page 1 of 11

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Modular - Written in routines called functions and classes (C++), can be reused in other applications or programs. Preferred by professional programmers - So, a variety of C/C++ resources and helpful supports are widely available. Standardized Many standards have been documented, maintained and updated for C and C++ as standard references for solving the portability and many other issues (please refer at the end of this tutorial).

1.3 Very Basic Program Development

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Computer program is designed to solve problem. Nowadays it makes ease a lot of our works. The simple steps to find a solution to problems are the same steps used to write a program and basically can be defined as follows: 1. 2. 3. 4. Define the problem. Devise a plan to solve it. Implement the plan. Test the result to see whether the problem is solved.

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When creating a program in C/C++: 1. 2. 3. 4. Determine the objective(s) of the program. Decide which method the program will use to solve the problem. Translate this method into a computer program using the C/C++ language. Run and test the program.

No

Typical steps might be followed in a program development is listed below:Step Description

1

Using an editor to enter the source code

2

Using a compiler

3

Creating an executable file

4

Running/executing the program

5

Debugging

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Release/Distribution

From a simple text editor up to complex Integrate Development Environment (IDE). Examples: UNIX: ed, ex, edit, emacs and vi. Window OS: notepad, Microsoft Visual Studio/.Net, Borland C++, Borland Turbo C++, Borland Builder C++, BorlandX. MSDOS: editor. OS/2: E or EPM editor. Computer cant understand the roman alphabets like English words. It only can understand machine language, 0s and 1s. The compiler perform this task, yields an object code (such as.obj or .o). C/C++ has function library that contains object code (codes that has been compiled) for predefined functions. These codes are ready to be used and can be called in the main program such as printf() function. They perform frequently needed tasks. Executable program can be run or executed. Before the executable program is created, a program called linker (to link other object and library files needed by the main program) performs a process called linking. Running the executable file/image. If there is no error, that is your program! (a running program or a process). Debug, debug and debug, finding program bugs, this is in debug mode. Alfa version - May still contains bugs, pre-release version. Beta / RC, Release Candidate version - May still contains bugs, prerelease version. Final release Release mode or release/Retail version (in reality, still have bugs:o)), but dont worry Patches and Service Packs will fix that.) Creating the installation program for distribution.

Typically, these basic steps are illustrated in figure 1.1 and quite a complete story can be found in Module W.

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Most of the editor used nowadays called Integrated Development Environment (IDE) that combines the process of compiling, linking, running, debugging, code validation, standard conformance and other functionalities in one environment such as Borland C++ Builder and Microsoft Visual Studio/.Net. Keep in mind that there are other extensions for the C/C++ program other than the .c, .cpp and .h. You have to check your compiler documentations or you can read the story in Module W of this Tutorial. Bear in mind also the real program development actually consist of a team of programmers, system analysts, project leader etc. Individually, how many lines of codes that we can write huh? So be real when you use this Tutorial for learning C and C++ :o).

1.4 Object Oriented Programming

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C++ is a C superset was developed by Bjarne Stroustrup at Bell Laboratories (some call advanced C) and the ANSI C++ (ISO/IEC C++) standard version is also already available. C++ provides a number of features that spruce up the C language mainly in the object-oriented programming aspects and data type safety (which lack in C language). Though if you have studied the C++, you will find that the type safety of the C++ also not so safe :o) actually the secure codes depend on the programmers themselves (C++ discussed in Tutorial #3). Object are essentially reusable software components that model items in the real world.

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1.5

Using a modular, object-oriented design and implementation, can speed up the program development and make the same software development group, up to many times more productive than the conventional programming techniques. Then, the evolution of the C++ continues with the introduction of the Standard Template Library (STL). STL deal mainly with data structure processing and have introduced the using of templates. From procedural programming to object oriented programming, STL has introduced generic programming. Then we have Common Language Runtime (CLR) type of the programming language, something like Java (through the Java Virtual Machine JVM) and the equivalent one from Microsoft is C#.

Sample of Simple Program Examples

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Let explore the basic structure of the C/C++ as shown in following section, before we proceed to the next Module. Dont worry about what the codes will do; just type or copy-paste and run the program. The program start with what is called preprocessor directive, #include. Then the main program start, with keyword main(), each program must have a main() function. All the coding is included in the body of the main program in the curly braces { } and } end the coding for the program. Try all the sample programs given. Be familiar with the writing codes, compiling, running and your IDE programming environment. Program Examples Warming up!

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Your task is to write the source code, compile and run. Notice that you only have to change some of the codes in the curly braces { } and adding or deleting the preprocessor directive to complete all the examples. Learn how to modify the program source code and re run the program. You will learn a lot more things! Please refer to the Kick Start: Using Compilers section, in order to write, compile and run your Win32 Console Mode Application program using Borland or Microsoft Visual Studio/.Net product or whatever compiler you are familiar with.Example #1

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For starting, first step we just create the program skeleton. Try to compile and run the simple program. Make sure there is no error. Notice the line of code that span on multiple lines. Keep it on one line. Dont worry about any syntax or standard violation; you will be prompted by your compiler through warnings and/or errors :o). Keep in mind that, typing the codes, is dealing with character set, laid out on your keyboard whether it is ASCII, EBCDIC, Unicode or proprietary character set :o). And C/C++ programs only deal with the characters, strings and mathematical expressions.

//The simplest program example //preprocessor directives - header files #include #include //main() function with no argument //and int return value int main( ) { cout\'\v\' \vTesting\n"); printf("The backslash --->\'\\\\' \\Testing\\\n"); printf("The single quote --->\'\'\' \'Testing\'\'\'\n"); printf("The double quote --->\'\"\' \"Testing\"\"\n"); printf("The question mark --->\'\?\' \?Testing\?\n"); printf("Some might not working isn't it?\n"); system("pause"); return 0; }

Output:

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Example #11#include #include int main() { int num; printf("Conversion...\n"); printf("Start with any character and\n"); printf("Press Enter, EOF to stop\n"); num = getchar(); printf("Character Integer Hexadecimal Octal\n"); while(getchar() != EOF) { printf(" %c %d %x %o\n",num,num,num,num); ++num; } system("pause"); return 0; }

Output:

Example #12#include #include /*convert decimal to binary function*/

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void dectobin(); int main() { char chs = 'Y'; do { dectobin(); printf("Again? Y, others to exit: "); chs = getchar(); scanf("%c", &chs); }while ((chs == 'Y') || (chs == 'y')); return 0; } void dectobin() { int input; printf("Enter decimal number: "); scanf("%d", &input); if (input < 0) printf("Enter unsigned decimal!\n"); /*for the mod result*/ int i; /*count the binary digits*/ int count = 0; /*storage*/ int binbuff[64]; do { /* Modulus 2 to get the remainder of 1 or 0*/ i = input%2; /* store the element into the array */ binbuff[count] = i; /* Divide the input by 2 for binary decrement*/ input = input/2; /* Count the number of binary digit*/ count++; /*repeat*/ }while (input > 0); /*prints the binary digits*/ printf ("The binary representation is: "); do { printf("%d", binbuff[count - 1]); count--; if(count == 8) printf(" "); } while (count > 0); printf ("\n"); }

Output:

Example #13#include #include /*for strlen*/ #include

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/*convert bin to decimal*/ void bintodec() { char buffbin[100]; char *bin; int i=0; int dec = 0; int bcount; printf("Please enter the binary digits, 0 or/and 1.\n"); printf("Your binary digits: "); bin = gets(buffbin); i=strlen(bin); for (bcount=0; bcount 0); printf ("\n"); }

Output:

Example #15/*Playing with binary, decimal, hexadecimal and octal conversion*/ #include #include /*strlen*/ #include /*decimal conversion function */ void decimal(char *deci, int *decires); /* convert decimal to binary*/ void decnumtobin (int *dec); int main()

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{ /* Yes or No value to continue with program */ char go; char choice1; char choice2; /*numtest, value to test with, and pass to functions*/ int numtest; /*value to convert to binary, and call decnumtobin function*/ int bintest; int flag; flag = 0; go = 'y'; do { printf ("Enter the h for hex input: "); scanf("%c", &choice1); getchar(); printf ("\n"); printf ("Enter your hex number lor!: "); /*If hexadecimal number*/ if ((choice1 == 'h') || (choice1 == 'H')) { scanf ("%x", &numtest); getchar(); } else { flag = 1; printf ("Only h!\n"); printf("Program exit...\n"); exit(0); } /*Firstly convert the input 'number' to binary*/ bintest = numtest; decnumtobin(&bintest); /*output the hex, decimal or octal*/ printf ("\n"); printf ("Enter the d for decimal output: "); scanf ("%c", &choice2); getchar(); /*If decimal number*/ if ((choice2 == 'd') || (choice2 == 'D')) decimal(&choice1, &numtest); /*else...*/ else { flag = 1; printf("Only d!"); printf("\nProgram exit..."); exit(0); } printf ("\n\n"); printf ("The program is ready to exit...\n"); printf ("Start again? (Y for Yes) : "); scanf ("%c", &go); getchar(); /*initialize to NULL*/ numtest = '\0'; choice1 = '\0'; choice2 = '\0'; } while ((go == 'y') || (go == 'Y')); printf ("-----FINISH-----\n"); return 0; } /*===================================================*/ void decimal(char *deci, int *decires) { int ans = *decires; char ch = *deci; if ((ch == 'h') || (ch == 'H'))

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printf ("\nThe number \"%X\" in hex is equivalent to \"%d\" in decimal.\n", ans, ans); } void decnumtobin (int *dec) { int input = *dec; int i; int count = 0; int binary[128]; do { /* Modulus 2 to get 1 or a 0*/ i = input%2; /* Load Elements into the Binary Array */ binary[count] = i; /* Divide input by 2 for binary decrement */ input = input/2; /* Count the binary digits*/ count++; }while (input > 0); /* Reverse and output binary digits */ printf ("The binary representation is: "); do { printf ("%d", binary[count - 1]); count--; if(count == 4) printf(" "); } while (count > 0); printf ("\n"); }

Output:

Example #16/*Playing with hexadecimal and ascii*/ #include #include /*strlen*/ #include /*decimal conversion function */ void decimal(int *decires); /*convert decimal to binary*/ void decnumtobin (int *dec); int main() { /*Program continuation...*/ char go; /* numtest, value to test with, and pass to functions*/ int numtest; /* value to convert to binary, and call decnumtobin function*/ int bintest; int flag = 0;

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go = 'y'; do { printf("Playing with hex and ASCII\n"); printf("==========================\n"); printf("For hex, 0(0) - 1F(32) are non printable/control characters!\n"); printf("For hex > 7F(127) they are extended ASCII characters that are\n"); printf("platform dependent!\n\n"); printf("Enter the hex input: "); scanf("%x", &numtest); getchar(); /*Firstly convert the input 'number' to binary*/ bintest = numtest; decnumtobin(&bintest); decimal (&numtest); printf("\nStart again? (Y for Yes) : "); scanf ("%c", &go); getchar(); /*initialize to NULL*/ numtest = '\0'; } while ((go == 'y') || (go == 'Y')); printf("-----FINISH-----\n"); return 0; } /*===================================================*/ void decimal(int *decires) { int ans = *decires; /*If < decimal 32...*/ if(ans < 32) { printf("hex < 20(32) equivalent to non printable/control ascii characters\n"); switch(ans) { case 0:{printf("hex 0 is NULL ascii");}break; case 1:{printf("hex 1 is SOH-start of heading ascii");}break; case 2:{printf("hex 2 is STX-start of text ascii");}break; case 3:{printf("hex 3 is ETX-end of text ascii");}break; case 4:{printf("hex 4 is EOT-end of transmission ascii");}break; case 5:{printf("hex 5 is ENQ-enquiry ascii");}break; case 6:{printf("hex 6 is ACK-acknowledge ascii");}break; case 7:{printf("hex 7 is BEL-bell ascii");}break; case 8:{printf("hex 8 is BS-backspace ascii");}break; case 9:{printf("hex 9 is TAB-horizontal tab ascii");}break; case 10:{printf("hex A is LF-NL line feed, new line ascii");}break; case 11:{printf("hex B is VT-vertical tab ascii");}break; case 12:{printf("hex C is FF-NP form feed, new page ascii");}break; case 13:{printf("hex D is CR-carriage return ascii");}break; case 14:{printf("hex E is SO-shift out ascii");}break; case 15:{printf("hex F is SI-shift in ascii");}break; case 16:{printf("hex 10 is DLE-data link escape ascii");}break; case 17:{printf("hex 11 is DC1-device control 1 ascii");}break; case 18:{printf("hex 12 is DC2-device control 2 ascii");}break; case 19:{printf("hex 13 is DC3-device control 3 ascii");}break; case 20:{printf("hex 14 is DC4-device control 4 ascii");}break; case 21:{printf("hex 15 is NAK-negative acknowledge ascii");}break; case 22:{printf("hex 16 is SYN-synchronous idle ascii");}break; case 23:{printf("hex 17 is ETB-end of trans. block ascii");}break; case 24:{printf("hex 18 is CAN-cancel ascii");}break; case 25:{printf("hex 19 is EM-end of medium ascii");}break; case 26:{printf("hex 1A is SUB-substitute ascii");}break; case 27:{printf("hex 1B is ESC-escape ascii");}break; case 28:{printf("hex 1C is FS-file separator ascii");}break; case 29:{printf("hex 1D is GS-group separator ascii");}break; case 30:{printf("hex 1E is RS-record separator ascii");}break; case 31:{printf("hex 1F is US-unit separator ascii");}break; } } else printf ("\nThe number \"%X\" in hex is equivalent to \"%c\" ascii character.\n", ans, ans); }

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void decnumtobin (int *dec) { int input = *dec; int i; int count = 0; int binary[128]; do { /* Modulus 2 to get 1 or a 0*/ i = input%2; /* Load Elements into the Binary Array */ binary[count] = i; /* Divide input by 2 for binary decrement */ input = input/2; /* Count the binary digits*/ count++; }while (input > 0); /* Reverse and output binary digits */ printf("The binary representation is: "); do { printf("%d", binary[count - 1]); count--; if(count == 4) printf(" "); } while (count > 0); printf("\n"); }

Output:

Example #17

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Program example compiled using VC++/VC++ .Net.//Using C code and header in C++... #include int main() { int num; printf("Conversion...\n"); printf("Start with any character and\n"); printf("Press Enter, EOF to stop\n"); num = getchar();

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printf("Character Integer Hexadecimal Octal\n"); while(getchar() != EOF) { printf(" %c %d %x %o\n", num, num, num, num); ++num; } return 0; }

Output:

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Program examples compiled using gcc.

/*Another data type program example*/ #include /*main function*/ int main() { int short int unsigned short int float char long unsigned long long int short unsigned short double float

p q r s t u v w x y z a b

= = = = = = = = = = = = =

2000; -120; 121; 21.566578; 'r'; 5678; 5678; -5678; -171; -71; 99; 88.12345; -3.245823;

/*positive integer data type*/ /*variation*/ /*variation*/ /*float data type*/ /*char data type*/ /*long positive integer data type*/ /*variation*/ /*-ve long integer data type*/ /*-ve integer data type*/ /*short -ve integer data type*/ /*variation*/ /*double float data type*/ /*float data type*/

printf("\t--Data type again--\n"); printf("\t-------------------\n"); printf("\n1. \"int\" sample: \t\t %d, the data size: %d bytes", p, sizeof(p)); printf("\n2. \"short\" int sample: \t %d, the data size: %d bytes", q, sizeof(q)); printf("\n3. \"unsigned short int\" sample: %d, the data size: %d bytes", r, sizeof(r)); printf("\n4. \"float\" sample: \t\t %.7f, the data size: %d bytes", s, sizeof(s)); printf("\n5. \"char\" sample: \t\t %c, the data size: %d byte", t, sizeof(t)); printf("\n6. \"long\" sample: \t\t %d, the data size: %d bytes", u, sizeof(u)); printf("\n7. \"unsigned long\" sample: \t %d, the data size: %d bytes", v, sizeof(v)); printf("\n8. negative \"long\" sample: \t %d, the data size: %d bytes", w, sizeof(w)); printf("\n9. negative \"int\" sample: \t %d, the data size: %d bytes", x, sizeof(x)); printf("\n10. negative \"short\" sample: \t %d, the data size: %d bytes", y, sizeof(y)); printf("\n11. unsigned \"short\" sample: \t %d, the data size: %d bytes", z, sizeof(z)); printf("\n12. \"double\" sample: \t\t %.4f, the data size: %d bytes", a, sizeof(a)); printf("\n13. negative \"float\" sample: \t %.5f, the data size: %d bytes\n", b, sizeof(b)); return 0; }

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[bodo@bakawali ~]$ gcc datatype.c -o datatype [bodo@bakawali ~]$ ./datatype--Data type again-------------------1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. "int" sample: 2000, the data size: 4 bytes "short" int sample: -120, the data size: 2 bytes "unsigned short int" sample: 121, the data size: 2 bytes "float" sample: 21.5665779, the data size: 4 bytes "char" sample: r, the data size: 1 byte "long" sample: 5678, the data size: 4 bytes "unsigned long" sample: 5678, the data size: 4 bytes negative "long" sample: -5678, the data size: 4 bytes negative "int" sample: -171, the data size: 4 bytes negative "short" sample: -71, the data size: 2 bytes unsigned "short" sample: 99, the data size: 2 bytes "double" sample: 88.1235, the data size: 8 bytes negative "float" sample: -3.24582, the data size: 4 bytes

#include #include /*convert decimal to binary function*/ void dectobin(); int main() { char chs = 'Y'; do { dectobin(); printf("Again? Y, others to exit: "); chs = getchar(); scanf("%c", &chs); }while ((chs == 'Y') || (chs == 'y')); return 0; } void dectobin() { int input; printf("Enter decimal number: "); scanf("%d", &input); if (input < 0) printf("Enter unsigned decimal!\n"); /*for the mod result*/ int i; /*count the binary digits*/ int count = 0; /*storage*/ int binbuff[64]; do { /* Modulus 2 to get the remainder of 1 or 0*/ i = input%2; /* store the element into the array */ binbuff[count] = i; /* Divide the input by 2 for binary decrement*/ input = input/2; /* Count the number of binary digit*/ count++; /*repeat*/ }while (input > 0); /*prints the binary digits*/ printf("The binary representation is: "); do { printf("%d", binbuff[count - 1]); count--; if(count == 8) printf(" "); } while (count > 0); printf ("\n"); }

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[bodo@bakawali ~]$ gcc binary.c -o binary [bodo@bakawali ~]$ ./binaryEnter decimal number: 64 The binary representation is: 1000000 Again? Y, others to exit: Y Enter decimal number: 128 The binary representation is: 10000000 Again? Y, others to exit: Y Enter decimal number: 32 The binary representation is: 100000 Again? Y, others to exit: Y Enter decimal number: 100 The binary representation is: 1100100 Again? Y, others to exit: N [bodo@bakawali ~]$ cat binary.c

----------------------------------------------------o0o--------------------------------------------------Further reading and digging:

1. 2.

The ASCII, EBCDIC and UNICODE character sets reference Table can be found here: Character sets Table. Check the best selling C / C++ books at Amazon.com.

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MODULE 3 STATEMENTS, EXPRESSIONS AND OPERATORS My Training Period:Abilities

hours

Able to understand and use: 3.1

Statements. Expressions. Operators. The Unary Mathematical Operators. The Binary Mathematical Operators. Precedence and Parentheses. Relational Operator. Expression and if Statement. Relational Expressions. Precedence of Relational Operators. Logical Operators. True and False Values. Precedence of Logical Operators. Compound Assignment Operators. The Conditional Operator (Ternary). The Bitwise operators. The Comma Operator.

Statements

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A statement is a complete instruction asking the computer to carry out some tasks. Normally written one per line, although some statements span multiple lines. Always end with a semicolon ( ; ), except for preprocessor directive such as #define and #include. For example: Evaluation direction x = 2 + 3;

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This statement instructs the computer to add 2 to 3 and assign the result to the variable x. C/C++ compiler is not sensitive to white spaces such as spaces, tabs and blank lines in the source code, within the statements. Compiler read a statement in the source code it looks for the characters and for the terminating semicolon and ignores the white space. For example, three of the following examples are same. x = 2 + or 3; or

x=2+3; x = 2 + 3; -

You can try compiling the following program example; the not so readable codes, then see whether it is valid or not.//Demonstrate unary operators prefix and postfix modes #include #include #include int main(){int a, b; a = b = 5; printf("postfix mode and prefix mode example\n"); printf("initial value, a = b = 5\n"); printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b); //Some comment here

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printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\n");system("pause");return 0;}

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Or something like this:

//Demonstrate unary operators prefix and postfix modes #include #include #include int main(){int a, b; a = b = 5; printf("postfix mode and prefix mode example\n"); printf("initial value, a = b = 5\n"); printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);/*Another comment here*/ //Some comment here printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b); /*Another comment here*/printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\npostfix mode, a-- = %d prefix mode, --b = %d", a--, --b);printf("\n");system("pause");return 0;}

Output:

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The most important thing here is the semicolon that defines a statement and codes such as preprocessor directive and comments that cannot be in the same line with other codes. See also how the white spaces have been ignored and how the compiler read the codes. But there is an exception: For Literal string constants, white space such as tabs and spaces are considered part of the string. A string is a series of characters or combination of more than one character. Literal string constants are strings that are enclosed within double quotes and interpreted literally by the compiler, space by space.

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Is legal but:

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To break a literal string constant line, use the backslash character ( \ ) just before the break, like this: printf("Hello, \ World");

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For C++ you can use the double quotation pair, " more than one line easily. For example:

"

for each literal string for each line, so can break

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cout"; cin>>list[i]; } //do the sorting... for(i=0; i", i); scanf("%d", &list[i]); } //do the sorting... for(i=0; i14 list's element #2 -->-21 list's element #3 -->-30 list's element #4 -->34 list's element #5 -->25 list's element #6 -->12 list's element #7 -->99 list's element #8 -->100 list's element #9 -->73 -30 -21 12 14 23 25 34 73 99 100

Sorted list, ascending:

/**********************array2.c********************/ /*Printing 3x3 array's subscript and their element*/ #include #define m 3 #define n 3

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int main() { int i, j; int x[m][n]; printf("\n3x3 arrays' subscripts and\n"); printf("their respective elements\n"); printf("--------------------------\n"); for(i=0; i>x1>>x2; // call the function pointed by ptr small // has the return value small = (*ptr)(x1, x2); coutdir /a Volume in drive C has no label. Volume Serial Number is E8E3-18E2 Directory of C:\Firstdir 04/18/2005 04/18/2005 04/18/2005 04/18/2005 03:09p . 03:09p .. 03:08p 0 first.txt 03:09p Secondir 1 File(s) 0 bytes 3 Dir(s) 1,326,395,392 bytes free

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Every directory has entries for these file name components. The file name component '.' refers to the directory itself, while the file name component '..' refers to its parent directory (the directory that contains the link for the directory in question). That is why if we want to change to the parent directory of the current working directory we just issue the 'cd ..' command for Linux and Windows. Then in Linux, to run a program named testrun in the current working directory we issue the following command: ./testrun

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As a special case, '..' in the root directory refers to the root directory itself, since it has no parent; thus '/..' is the same as /. Here are some examples of file names:File name /a /a/b a /a/./b ./a ../a Description The file named a, in the root directory. The file named b, in the directory named a in the root directory. The file named a, in the current working directory. This is the same as /a/b. The file named a, in the current working directory. The file named a, in the parent directory of the current working directory. Table 9.1: File names examples

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A file name that names a directory may optionally end in a /. You can specify a file name of / to refer to the root directory, but the empty string is not a meaningful file name. If you want to refer to the current working directory, use a file name of '.' or './'. For example to run a program named testprog that located in the current working directory we just prefixes the ./ to the program name. ./testprog

9.4.3 Streams and FILE structure

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The type of the C data structure that represents a stream is called FILE rather than "stream". Since most of the library functions deal with objects of type FILE *, sometimes the term file pointer is also used to mean "stream". This leads to confusion over terminology in many reference materials and books on C. The FILE type is declared in the stdio.h header file.FILE data type This is the data type used to represent stream objects. A FILE object holds all of the internal state information about the connection to the associated file, including such things as the file position indicator and buffering information. Each stream also has error and end-of-file status indicators that can be tested with the ferror and feof functions. Table 9.2: FILE data type

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FILE objects are allocated and managed internally by the I/O library functions.

9.4.4 Standard Streams

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When the main function of your program is invoked, it already has three predefined streams open and available for use. These represent the standard input and output channels that have been established for the process. A process here means a running program. These streams are declared in the stdio.h header file and summarized in the following Table.Standard stream FILE * stdin FILE * stdout FILE * stderr Description The standard input stream variable, which is the normal source of input for the program. The standard output stream variable, which is used for normal output from the program. The standard error stream variable, which is used for error messages and diagnostics issued by the program. Table 9.3: Standard streams

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In the Linux system, you can specify what files or processes correspond to these streams using the pipe and redirection facilities provided by the shell. Most other operating systems provide similar mechanisms, but the details of how to use them can vary. In the GNU C library, stdin, stdout, and stderr are normal variables which you can set just like any others. For example, to redirect the standard output to a file, you could do:fclose(stdout); stdout = fopen ("standard-output-file", "w");

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However, in other systems stdin, stdout, and stderr are macros instead of variables that you cannot assign to in the normal way. But you can use for example freopen() function to get the effect of closing one and reopening it.

9.5 Links Story 9.5.1 Hard Links

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In POSIX systems, one file can have many names at the same time. All of the names are equally real, and no one of them is preferred to the others. In Windows it is called shortcuts. To add a name to a file, use the link() function (The new name is also called a hard link to the file). Creating a new link to a file does not copy the contents of the file; it simply makes a new name by which the file can be known, in addition to the file's existing name or names. One file can have names in several directories, so the organization of the file system is not a strict hierarchy or tree. In most implementations, it is not possible to have hard links to the same file in multiple file systems. link() reports an error if you try to make a hard link to the file from another file system when this cannot be done. The prototype for the link() function is declared in the header file unistd.h and is summarized below.int link(const char *oldname, const char *newname) The link function makes a new link to the existing file named by oldname, under the new name newname. This function returns a value of 0 if it is successful and -1 on failure. In addition to the usual file name errors, for both oldname and newname, the following errno error conditions are defined for this function: EACCES You are not allowed to write to the directory in which the new link is to be written. There is already a file named newname. If you want to replace this link with a new link, you EEXIST must remove the old link explicitly first. There are already too many links to the file named by oldname. (The maximum number of EMLINK links to a file is LINK_MAX). ENOENT The file named by oldname doesn't exist. You can't make a link to a file that doesn't exist. ENOSPC The directory or file system that would contain the new link is full and cannot be extended. In the GNU system and some others, you cannot make links to directories. Many systems EPERM allow only privileged users to do so. This error is used to report the problem. The directory containing the new link can't be modified because it's on a read-only file EROFS system. EXDEV The directory specified in newname is on a different file system than the existing file. EIO A hardware error occurred while trying to read or write the to filesystem. Table 9.4: link() function

9.5.2 Symbolic Links

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The Linux system for example, supports soft links or symbolic links. This is a kind of "file" that is essentially a pointer to another file name. Unlike hard links, symbolic links can be made to directories or across file systems with no restrictions. You can also make a symbolic link to a name which is not the name of any file. (Opening this link will fail until a file by that name is created). Likewise, if the symbolic link points to an existing file which is later deleted, the symbolic link continues to point to the same file name even though the name no longer names any file. The reason symbolic links work the way they do is that special things happen when you try to open the link. The open() function realizes you have specified the name of a link, reads the file name contained in the link, and opens that file name instead. The stat() function (used for file attributes information) likewise operates on the file that the symbolic link points to, instead of on the link itself. By contrast, other operations such as deleting or renaming the file operate on the link itself. The functions readlink() and lstat() also refrain from following symbolic links, because their purpose is to obtain information about the link. link(), the function that makes a hard link, does too. It makes a hard link to the symbolic link, which one rarely wants. Some systems have for some functions operating on files have a limit on how many symbolic links are allowed when resolving a path name. The limit if exists is published in the sys/param.h header file. The following lists functions and macros used for links.int MAXSYMLINKS The macro MAXSYMLINKS specifies how many symlinks some function will follow before returning ELOOP. Not all functions behave the same and this value is not the same as a returned for _SC_SYMLOOP by sysconf. In fact, the sysconf result can indicate that

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there is no fixed limit although MAXSYMLINKS exists and has a finite value. Table 9.5: MAXSYMLINKS macro

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Prototypes for most of the functions listed in the following section are in unistd.h.int symlink(const char *oldname, const char *newname) The symlink function makes a symbolic link to oldname named newname. The normal return value from symlink is 0. A return value of -1 indicates an error. In addition to the usual file name prototype errors (see File Name Errors), the following errno error conditions are defined for this function: EEXIST There is already an existing file named newname. EROFS The file newname would exist on a read-only file system. ENOSPC The directory or file system cannot be extended to make the new link. EIO A hardware error occurred while reading or writing data on the disk. Table 9.6: symlink() function int readlink(const char *filename, char *buffer, size_t size) The readlink function gets the value of the symbolic link filename. The file name that the link points to is copied into buffer. This file name string is not null-terminated; readlink normally returns the number of characters copied. The size argument specifies the maximum number of characters to copy, usually the allocation size of buffer. If the return value equals size, you cannot tell whether or not there was room to return the entire name. A value of -1 is returned in case of error. In addition to the usual file name errors, following errno error conditions are defined for this function: EINVAL The named file is not a symbolic link. EIO A hardware error occurred while reading or writing data on the disk. Table 9.7: readlink() function

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9.6 9.6.1

In some situations it is desirable to resolve all the symbolic links to get the real name of a file where no prefix, names a symbolic link which is followed and no filename in the path is '.' or '..'. This is for example desirable if files have to be compared in which case different names can refer to the same inode. For Linux system we can use canonicalize_file_name() function for this purpose. The UNIX standard includes a similar function which differs from canonicalize_file_name() in that the user has to provide the buffer where the result is placed in. It uses realpath() function. The advantage of using this function is that it is more widely available. The drawback is that it reports failures for long path on systems which have no limits on the file name length.

The Basic Of Disk File I/O Opening And Closing A Disk File

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Before we dive into the details, take note that the program examples presented here just for basic file I/O that applies to DOS and Linux. For Windows, you have to study the Win32 programming that provides specifics file I/O and other related functions. Here we do not discuss in details regarding the permission, right and authorization such as using Discretionary Access Control List (DACL) and Security Access Control List (SACL) implemented in Windows OS. Furthermore for DOS type OS also, Microsoft uses Microsoft C (C Runtime CRT). Nevertheless the concepts still apply to any implementation. As explained before, in C, a FILE structure is a file control structure defined in the header file stdio.h. A pointer of type FILE is called a file pointer, which references a disk file. A file pointer is used by stream to conduct the operation of the I/O functions. For instance, the following declaration defines a file pointer called fpter: FILE *fpter;

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In the FILE structure there is a member, called the file position indicator, which points to the position in a file where data will be read from or written to. The I/O function fopen() gives you the ability to open a file and associate a stream to the opened file. You need to specify the way to open a file and the filename with the fopen() function. The prototype is: FILE *fopen(const char *filename, const char *mode);

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Here, filename is a char pointer that references a string of a filename. The filename is given to the file that is about to be opened by the fopen() function. mode points to another string that specifies the way to open the file. The fopen() function returns a pointer of type FILE. If an error occurs during the procedure to open a file, the fopen() function returns a null pointer. Table 9.8 shows the possible ways to open a file by various strings of modes. Note that, you might see people use the mode rb+ instead of r+b. These two strings are equivalent. Similarly, wb+ is the same as w+b, ab+ is equivalent to a+b. The following program segment example try to open a file named test.txt, located in the same folder as the main() program for reading.FILE *fptr; if((fptr = fopen("test.txt","r")) == NULL) { printf("Cannot open test.txt file.\n"); exit(1); }

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Here, "r" is used to indicate that the text file is about to be opened for reading only. If an error occurs such as the file is non-exist, when the fopen() function tries to open the file, the function returns a null pointer. Then an error message is printed out by the printf() function and the program is aborted by calling the exit() function with a nonzero value to handle the exception.Mode r w a r+ w+ a+ rb wb ab r+b w+b a+b Description Open a file for reading. Create a file for writing. If the file already exists, discard the current contents. Append, open or create a file for writing at the end of the file. Open a file for update (reading and writing). Create a file for update. If the file already exists, discard the current contents. Append, open or create a file for update, writing is done at the end of the file. Opens an existing binary file for reading. Creates a binary file for writing. Opens an existing binary file for appending. Opens an existing binary file for reading or writing. Creates a binary file for reading or writing. Opens or creates a binary file for appending. Table 9.8: Possible ways opening a file by various strings of modes in C

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After a disk file is read, written, or appended with some new data, you have to disassociate the file from a specified stream by calling the fclose() function. The prototype for the fclose() function is: int fclose(FILE *stream);

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Here, stream is a file pointer that is associated with a stream to the opened file. If fclose() closes a file successfully, it returns 0. Otherwise, the function returns EOF. By assuming the previous program segment successfully opened the test.txt for reading, then to close the file pointer we should issue the following code: fclose(fptr);

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Normally, the fclose() function fails only when the disk is removed before the function is called or there is no more space left on the disk. The end-of-file (EOF) combination key for different platform is shown in table 9.9. You have to check your system documentation.Computer system UNIX systems IBM PC and compatibles Macintosh - PowerPC VAX (VMS) Key combination

d z d z

Table 9.9: End-of-file (EOF) key combinations for various computer systems.

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Since all high-level I/O operations are buffered, the fclose() function flushes data left in the buffer to ensure that no data will be lost before it disassociates a specified stream with the opened file. A file that is opened and associated with a stream has to be closed after the I/O operation. Otherwise, the data saved in the file may be lost or some unpredictable errors might occur during the next time file opening. Let try the following program example, which shows you how to open and close a text file and how to check the returned file pointer value as well. First of all you have to create file named tkk1103.txt. This file must be in the same folder as your running program, or you have to provide the full path string if you put it in other folder. By default program will try finding file in the same folder where the program is run. For example, if you run your C program in folder:C:\BC5\Myproject\testing\

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Then, make sure you put the tkk1103.txt file in the same folder:C:\BC5\Myproject\testing\tkk1103.txt1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. //Opening and closing file example #include #include //SUCCESS = 0, FAIL = 1 using enumeration enum {SUCCESS, FAIL}; int main (void) { FILE *fptr; //the filename is tkk1103.txt and located //in the same folder as this program char filename[] = "tkk1103.txt"; //set the value reval to 0 int reval = SUCCESS; //test opening file for reading, if fail... if((fptr = fopen(filename, "r")) == NULL) { printf("Cannot open %s.\n", filename); reval = FAIL; //reset reval to 1 } //if successful do... else { printf("Opening the %s file successfully\n", filename); //the program will display the address where //the file pointer points to.. printf("The value of fptr: 0x%p\n", fptr); printf("\n....file processing should be done here....\n"); printf("\nReady to close the %s file.\n", filename); //close the file stream... if(fclose(fptr)==0) printf("Closing the %s file successfully\n", filename); } //for Borlandcan remove the following pause and the library, //stdlib.h for other compilers system("pause"); return reval; Page 9 of 34

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40. }

40 lines: Output:

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If opening the file is fails, the following will be output:

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Remember, for the "r" mode, you have to create and save tkk1103.txt file in the same folder where the .exe file for this program resides or provide the full path strings in the program. This program shows you how to open a text file. fopen() function tries to open a text file with the name contained by the string array filename for reading. The filename (stored in array) is defined and initialized with to tkk1103.txt. If an error occurs when you try to open the text file, the fopen() function returns a null pointer. Next line then prints a warning message, and assigns the value represented by the enum name FAIL to the int variable reval. From the declaration of the enum data type, we know that the value of FAIL is 1. However, if the fopen() function opens the text file successfully, the following statement:printf("The value of fptr: 0x%p\n", fptr);

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Will print the value contained by the file pointer fptr. At the end line of code tells the user that the program is about to close the file, and then fclose(fptr); closes the file by calling the fclose() file. return reval; the return statement returns the value of reval that contains 0 if the text file has been opened successfully or 1 otherwise. From the output, the value held by the file pointer is 0x0D96:01C2 (memory address) after the text file is open successfully. Different pc will have different address. If your tkk1103.txt file is not in same folder as your main() program, you have to explicitly provide the full path of the file location. For example, if your tkk1103.txt is located in C:\Temp folder, you have to change:char filename[] = "tkk1103.txt";

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Tochar filename[] = "c:\\Temp\\tkk1103.txt";

9.6.2

Reading And Writing Disk File

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The previous program example does not do anything with the text file, tkk1103.txt, except open and close it. Some text has been saved in tkk1103.txt, so how can you read them from the file? In C you can perform I/O operations in the following ways: 0. 0. Read or write one character at a time. Read or write one line of text (that is, one line of characters) at a time.Page 10 of 34

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0.9.6.2.1

Read or write one block of characters at a time.

One Character At A Time

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Among the C I/O functions, there is a pair of functions, fgetc() and fputc(), that can be used to read from or write to a disk file one character at a time. The prototype for the fgetc() function is: int fgetc(FILE *stream);

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The stream is the file pointer that is associated with a stream. The fgetc() function fetches the next character from the stream specified by stream. The function then returns the value of an int that is converted from the character. The prototype for the fputc() function is: int fputc(int c, FILE *stream);

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c is an int value that represents a character. In fact, the int value is converted to an unsigned char before being output. stream is the file pointer that is associated with a stream. The fputc() function returns the character written if the function is successful, otherwise, it returns EOF. After a character is written, the fputc() function advances the associated file pointer. Let explore the program example. Before that, you have to create two text files named, testone.txt and testtwo.txt then save it in the same folder where the your main() program is or provide the full path strings if the files is in another folder. Then for file testtwo.txt, write the following texts and save itOPENING, READING, WRITING AND CLOSING FILE ------------------------------------------Testing file. This file named testtwo.txt. After opening files for reading and writing, without error, content of this file (testtwo.txt) will be read and output (write) to the other file named testone.txt and standard output(screen/console) character by character!!! ---HAPPY LEARNING FOLKS!!!----

Content of file testtwo.txt

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Then, if you run the program with no error, modify the content of the testtwo.txt, recompile and rerun the program. The displaying texts and the content of testone.txt also will change. Next check also the content of testone.txt file, the content should be same as testtwo.txt file and the texts displayed on your screen.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. //Reading and writing one character at a time #include #include //enumerated data type, SUCCESS = 0, FAIL = 1 enum {SUCCESS, FAIL}; //prototype function for reading from and writing... void CharReadWrite(FILE *fin, FILE *fout); int main() { //declare two file pointers... FILE *fptr1, *fptr2; //define the two files name... char filename1[] = "testone.txt"; char filename2[] = "testtwo.txt"; int reval = SUCCESS; //test the opening filename1 for writing.... //if fails.... if ((fptr1 = fopen(filename1, "w")) == NULL) { printf("Problem, cannot open %s.\n", filename1); reval = FAIL; } Page 11 of 34

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27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65.

//if opening filename1 for writing is successful, //test for opening for reading filename2, if fails... else if ((fptr2 = fopen(filename2, "r")) == NULL) { printf("Problem, cannot open %s.\n", filename2); reval = FAIL; } //if successful opening for reading from filename2 //and writing to filename1... else { //function call for reading and writing... CharReadWrite(fptr2, fptr1); //close both files... if(fclose(fptr1)==0) printf("%s closed successfully\n", filename1); if(fclose(fptr2)==0) printf("%s closed successfully\n", filename2); } //For Borland if compiled using its IDE system("pause"); return reval; } //read write function definition void CharReadWrite(FILE *fin, FILE *fout) { int c; //if the end of file is reached, do... while ((c = fgetc(fin)) != EOF) { //write to a file... fputc(c, fout); //display on the screen... putchar(c); } printf("\n"); }

65 lines: Output:

9.6.2.2

This program read one character from a file, writes the character to another file, and then display the character on the screen.One Line At A Time

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Besides reading or writing one character at a time, you can also read or write one character line at time. There is a pair of C I/O functions, fgets() and fputs(), that allows you to do so. The prototype for the fgets() function is: char *fgets(char *s, int n, FILE *stream);

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s, references a character array that is used to store characters read from the opened file pointed to by the file pointer stream. n specifies the maximum number of array elements. If it is successful, the fgets() function returns the char pointers s. If EOF is encountered, the fgets() function

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returns a null pointer and leaves the array untouched. If an error occurs, the function returns a null pointer, and the contents of the array are unknown. The fgets() function can read up to n-1 characters, and can append a null character after the last character fetched, until a newline or an EOF is encountered. If a newline is encountered during the reading, the fgets() function includes the newline in the array. This is different from what the gets() function does. The gets() function just replaces the newline character with a null character. The prototype for the fputs() function is: int fputs(const char *s, FILE *stream);

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s points to the array that contains the characters to be written to a file associated with the file pointer stream. The const modifier indicates that the content of the array pointed to by s cannot be changed. If it fails, the fputs() function returns a nonzero value, otherwise, it returns zero. The character array must include a null character at the end as the terminator to the fputs() function. Also, unlike the puts() function, the fputs() function does not insert a newline character to the string written to a file. Let try a program example. First of all, create two text file named testhree.txt and testfour.txt and put it under folder C:\. File testfour.txt should contain the following texts:OPENING, READING, WRITING one line of characters ---------------------------------------------------This is file testfour.txt. This file's content will be read line by line of characters till no more line of character found. Then, it will be output to the screen and also will be copied to file testhree.txt. Check the content of testhree.txt file... ---------------------------------------------------------------------HAVE A NICE DAY-------------------

Content of testfour.txt file1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. //Reading and writing one line at a time #include #include enum {SUCCESS, FAIL, MAX_LEN = 100};

//function prototype for read and writes by line... void LineReadWrite(FILE *fin, FILE *fout); int main(void) { FILE *fptr1, *fptr2; //file testhree.txt is located at the root, c: //you can put this file at any location provided //you provide the full path, same for testfour.txt char filename1[] = "c:\\testhree.txt"; char filename2[] = "c:\\testfour.txt"; char reval = SUCCESS; //test opening testhree.txt file for writing, if fail... if((fptr1 = fopen(filename1,"w")) == NULL) { printf("Problem, cannot open %s for writing.\n", filename1); reval = FAIL; } //test opening testfour.txt file for reading, if fail... else if((fptr2=fopen(filename2, "r"))==NULL) { printf("Problem, cannot open %s for reading.\n", filename2); reval = FAIL; } //if opening fro writing and reading successful, do... else { //function call for read and write, line by line... LineReadWrite(fptr2, fptr1);

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39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62.

//close both files stream... if(fclose(fptr1)==0) printf("%s successfully closed.\n", filename1); if(fclose(fptr2)==0) printf("%s successfully closed.\n", filename2); } //For Borland screenshot system("pause"); return reval; } //function definition for line read, write void LineReadWrite(FILE *fin, FILE *fout) { //local variable... char buff[MAX_LEN]; while(fgets(buff, MAX_LEN, fin) !=NULL) { //write to file... fputs(buff, fout); //write to screen... printf("%s", buff); } }

62 lines: Output:

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In this program example, the text files are located in C:\ drive. The fgets() function is called repeatedly in a while loop to read one line of characters at a time from the testfour.txt file, until it reaches the end of the text file. In line 54, the array name buff and the maximum number of the array elements MAX_LEN are passed to the fgets() function, along with the file pointer fin that is associated with the opened testfour.txt file. Meanwhile, each line read by the fgets() function is written to another opened text file called testhree.txt that is associated with the file pointer fout. This is done by invoking the fputs() function in line 58. The statement in line 60 prints the contents of each string on the screen so that you see the contents of the testfour.txt file. You also can view the testhree.txt file content in a text editor to make sure that the contents of the testfour.txt file have been copied to the testhree.txt file.One Block At A Time

9.6.2.3

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You can also read or write a block of data at a time. There are two C I/O functions, fread() and fwrite(), that can be used to perform block I/O operations. The prototype for the fread() function is:size_t fread(void *ptr, size_t size, size_t n, FILE *stream);

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The ptr is a pointer to an array in which the data is stored. size indicates the size of each array element. n specifies the number of elements to be read. stream is a file pointer that is associated with the opened file for reading.

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size_t is an integral type defined in the header file stdio.h. The fread() function returns the number of elements actually read. The number of elements read by the fread() function should be equal to the value specified by the third argument to the function, unless an error occurs or an EOF is encountered. The fread() function returns the number of elements that are actually read, if an error occurs or an EOF is encountered. The prototype for the fwrite() function is:size_t fwrite(const void *ptr, size_t size, size_t n, FILE *stream);

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ptr references the array that contains the data to be written to an opened file pointed to by the file pointer stream. size indicates the size of each element in the array. n specifies the number of elements to be written. The fwrite() function returns the number of elements actually written. If there is no error occurring, the number returned by fwrite() should be the same as the third argument in the function. The return value may be less than the specified value if an error occurs. That is the programmers responsibility to ensure that the array is large enough to hold data for either the fread() function or the fwrite() function. In C, a function called feof() can be used to determine when the end of a file is encountered. This function is more useful when you are reading a binary file because the values of some bytes may be equal to the value EOF. If you determine the end of a binary file by checking the value returned by fread(), you may end up at the wrong position. Using the feof() function helps you to avoid mistakes in determining the end of a file. The prototype for the feof() function is: int feof(FILE *stream);

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Here, stream is the file pointer that is associated with an opened file. The feof() function returns 0 if the end of the file has not been reached, otherwise, it returns a nonzero integer. Let take a look at the program example. Create two files named it testfive.txt and testsix.txt in C:\Temp folder or other folder that you choose provided that you provide the full path strings in the program. Write the following texts into testsix.txt file and save it.OPENING, READING AND WRITING ONE BLOCK OF DATA ----------------------------------------------This is file testsix.txt. Its content will be read and then output to the screen/console and copied to testfive.txt file. The reading and writing based on block of data. May be this method is faster compared to read/write by character, by line..... ----------------------------------------------------------------END--------------------------

Content of testsix.txt file1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. //Reading and writing one block at a time #include #include //declare enum data type, you will this //learn in other module... enum {SUCCESS, FAIL, MAX_LEN = 80}; //function prototype for block reading and writing void BlockReadWrite(FILE *fin, FILE *fout); //function prototype for error messages... int ErrorMsg(char *str); int main(void) { FILE *fptr1, *fptr2; //define the filenames... //the files location is at c:\Temp char filename1[] = "c:\\Temp\\testfive.txt"; char filename2[] = "c:\\Temp\\testsix.txt"; int reval = SUCCESS; Page 15 of 34

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//test opening testfive.txt file for writing, if fail... if((fptr1 = fopen(filename1, "w")) == NULL) { reval = ErrorMsg(filename1); } //test opening testsix.txt file for reading, if fail... else if ((fptr2 = fopen(filename2, "r")) == NULL) { reval = ErrorMsg(filename2); } //if opening files for writing and reading is successful, do... else { //call function for reading and writing BlockReadWrite(fptr2, fptr1); //close both files streams... if(fclose(fptr1)==0) printf("%s successfully closed\n", filename1); if(fclose(fptr2)==0) printf("%s successfully closed\n", filename2); } printf("\n"); //for Borland... system("pause"); return reval; } //function definition for block read, write void BlockReadWrite(FILE *fin, FILE *fout) { int num; char buff[MAX_LEN + 1]; //while not end of file for input file, do... while(!feof(fin)) { //reading... num = fread(buff, sizeof(char), MAX_LEN, fin); //append a null character buff[num * sizeof(char)] = '\0'; printf("%s", buff); //writing... fwrite(buff, sizeof(char), num, fout); } } //function definition for error message int ErrorMsg(char *str) { //display the error message... printf("Problem, cannot open %s.\n", str); return FAIL; }

75 lines: Output:

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Note the use of fread() and fwrite() functions in the program. This program shows you how to invoke the fread() and fwrite() to perform block I/O operations.Page 16 of 34

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The testsix.txt file is read by the fread() function, and the fwrite() function used to write the contents read from testsix.txt to another file called testfive.txt.

9.7 Random Access To Disk Files

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Before this you have learned how to read or write data sequentially. In many cases, however, you may need to access particular data somewhere in the middle of a disk file. Random access is another way to read and write data to disk file. Specific file elements can be accessed in random order. There are two C I/O functions, fseek() and ftell(), that are designed to deal with random access. You can use the fseek() function to move the file position indicator to the spot you want to access in a file. The prototype for the fseek() function is: int fseek(FILE *stream, long offset, int whence);

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stream is the file pointer with an opened file. offset indicates the number of bytes from a fixed position, specified by whence, that can have one of the following integral values represented by SEEK_SET, SEEK_CUR and SEEK_END. If it is successful, the fseek() function return 0, otherwise the function returns a nonzero value. whence provides the offset bytes from the file location. whence must be one of the values 0, 1, or 2 which represent three symbolic constants (defined in stdio.h) as follows:Constants SEEK_SET SEEK_CUR SEEK_END whence 0 1 2 File location

File beginning Current file pointer position End of file

Table 9.10: offset bytes

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If SEEK_SET is chosen as the third argument to the fseek() function, the offset is counted from the beginning of the file and the value of the offset is greater than or equal to zero. If however, SEEK_END is picked up, then the offset starts from the end of the file, the value of the offset should be negative. When SEEK_CUR is passed to the fseek() function, the offset is calculated from the current value of the file position indicator. You can obtain the value of the current position indicator by calling the ftell() function. The prototype for the ftell() function is, long ftell(FILE *stream);

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stream is the file pointer associated with an opened file. The ftell() function returns the current value of the file position indicator. The value returned by the ftell() function represents the number of bytes from the beginning of the file to the current position pointed to by the file position indictor. If the ftell() function fails, it returns 1L (that is, a long value of minus 1). Let explore the program example. Create and make sure text file named tesseven.txt is located in the C:\Temp folder before you can execute the program. The contents of the tesseven.txt is,THIS THIS THIS THIS IS IS IS IS THE THE THE THE FIRST LINE OF TEXT, tesseven.txt file SECOND LINE OF TEXT, tesseven.txt file THIRD LINE OF TEXT, tesseven.txt file FOURTH LINE OF TEXT, tesseven.txt file

The content of tesseven.txt file1. 2. 3. 4. 5. 6. 7. 8. //Random access to a file #include #include enum {SUCCESS, FAIL, MAX_LEN = 120};

//function prototypes, seek the file position indicator void PtrSeek(FILE *fptr); Page 17 of 34

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//function prototype, tell the file position indicator long PtrTell(FILE *fptr); //function prototype read and writes void DataRead(FILE *fptr); int ErrorMsg(char *str); int main(void) { FILE *fptr; char filename[] = "c:\\Temp\\tesseven.txt"; int reval = SUCCESS; //if there is some error opening file for reading if((fptr = fopen(filename, "r")) == NULL) { reval = ErrorMsg(filename); } //if opening is successful else { //PtrSeek() function call PtrSeek(fptr); //close the file stream if(fclose(fptr)==0) printf("%s successfully closed.\n", filename); } //for Borland... system("pause"); return reval; } //PtrSeek() function definition void PtrSeek(FILE *fptr) { long offset1, offset2, offset3, offset4; offset1 = PtrTell(fptr); DataRead(fptr); offset2 = PtrTell(fptr); DataRead(fptr); offset3 = PtrTell(fptr); DataRead(fptr); offset4 = PtrTell(fptr); DataRead(fptr); printf("\nReread the //reread the 2nd line fseek(fptr, offset2, DataRead(fptr); //reread the 1st line fseek(fptr, offset1, DataRead(fptr); //reread the 4th line fseek(fptr, offset4, DataRead(fptr); //reread the 3rd line fseek(fptr, offset3, DataRead(fptr); } //PtrTell() function definition long PtrTell(FILE *fptr) { long reval; //tell the fptr position reval = ftell(fptr); printf("The fptr is at %ld\n", reval); return reval; } //DataRead() function definition void DataRead(FILE *fptr) { char buff[MAX_LEN]; //reading line of text at the fptr position fgets(buff, MAX_LEN, fptr); //and display the text printf("-->%s\n", buff); } tesseven.txt, in random order:\n"); of the tesseven.txt SEEK_SET); of the tesseven.txt SEEK_SET); of the tesseven.txt SEEK_SET); of the tesseven.txt SEEK_SET);

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89. 90. 91. 92. 93. 94. 95.

//Error message function definition int ErrorMsg(char *str) { //display this error message printf("Problem, cannot open %s.\n", str); return FAIL; }

95 lines: Output:

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We try to open the tesseven.txt file for reading by calling the fopen() function. If successful, we invoke the PtrSeek() function with the fptr file pointer as the argument in line 30.PtrSeek(fptr);

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The definition of our first function PtrSeek() is shown in lines 41-67. The statement in line 45 obtains the original value of the fptr file pointer by calling another function, PtrTell(), which is defined in lines 7077. The PtrTell() function can find and print out the value of the file position indicator with the help of the ftell() function. The third function, DataRead() is called to read one line of characters from the opened file and print out the line of characters on the screen. Line 47 gets the new value of the fptr file position indicator right after the reading and assigns the value to another long variable, offset2. Then the DataRead() function in line 48 reads the second line of characters from the opened file. Line 49 obtains the value of the file position indicator that points to the first byte of the third line and assigns the value to the third long variable offset3 and so on for the fourth line of text. Line 50 calls the DataRead() function to read the third line and print it out on the screen. From the first portion of the output, you can see the four different values of the file position indicator at four different positions, and the four lines of texts. The four values of the file position indicator are saved by offset1, offset2, offset3 and offset4 respectively. Then, we read the lines of text randomly, one line at a time. Firstly read the second line, then the first line, fourth and finally the third one. C function, called rewind(), can be used to rewind the file position indicator. The prototype for the rewind() function is: void rewind(FILE *stream);

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Here, stream is the file pointer associated with an opened file. No value is returned by rewind() function. In fact the following statement of rewind() function:

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rewind(fptr); Is equivalent to this: (void) fseek(fptr, 0L, SEEK_SET); The void data type is cast to the fseek() function because the rewind() function does not return a value. Study the following program example. This program also contains example of reading and writing binary data. We create and open the teseight.bin file for writing.//Reading, writing, rewind and binary data #include #include enum {SUCCESS, FAIL, MAX_NUM = 5};

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//functions prototype... void DataWrite(FILE *fout); void DataRead(FILE *fin); int ErrorMsg(char *str); int main(void) { FILE *fptr; //binary type files... char filename[] = "c:\\Temp\\teseight.bin"; int reval = SUCCESS; //test for creating, opening binary file for writing... if((fptr = fopen(filename, "wb+")) == NULL) { reval = ErrorMsg(filename); } else { //Write data into file teseight.bin DataWrite(fptr); //reset the file position indicator... rewind(fptr); //read data... DataRead(fptr); //close the file stream... if(fclose(fptr)==0) printf("%s successfully closed\n", filename); } //for Borland system("pause"); return reval; } //DataWrite() function definition void DataWrite(FILE *fout) { int i; double buff[MAX_NUM] = { 145.23, 589.69, 122.12, 253.21, 987.234}; printf("The size of buff: %d-byte\n", sizeof(buff)); for(i=0; i