Structure Programming Programming in Java Instructed and enhanced by Dr. Safia Abbas Computer Science Department Faculty of Computer and Information Sciences

Structure ProgrammingProgramming in Java

Instructed and enhanced byDr. Safia Abbas

Computer Science DepartmentFaculty of Computer and Information Sciences

Ain Shams University

Prepared By

Dr. safia abbasComputer Science Department

Faculty of Computer and Information SciencesAin Shams University

1

• Instructor: Dr. safia abbas

• Text Book: • Paul Deitel and Harvey Deitel. “Java-How to Program. 9th edition, Pearson,2013.”

The Course

How to Think Like a Computer Scientist http://greenteapress.com/thinkapjava/thinkapjava.pdf

Introduction to Programming Using Java, 5th Edition http://math.hws.edu/javanotes/

Thinking in Java, 3rd Edition http://nyll.com/ebooks/index.html

Sun Java Tutorial http://download.oracle.com/javase/tutorial/java/

The Java API http://download.oracle.com/javase/1.5.0/docs/api/

Other (Online) Resources

http://greenteapress.com/thinkapjava/thinkapjava.pdf

http://math.hws.edu/javanotes/

http://nyll.com/ebooks/index.html

http://download.oracle.com/javase/tutorial/java/

http://download.oracle.com/javase/1.5.0/docs/api/

Course Contents

• Introduction.• Variables, types and expressions.• Functions and procedural abstraction.• Input/ output and streams.• Branch and loop statements.• Arrays and strings.• Pointers.• Recursions.

Lecture 1: Agenda • Introduction - computer hardware & Programming Languages

• First Program• Output Using pint• Directives• Comments

• Integer Variables• Input with Scanner• Variable Names• Arithmetic Expressions

• The arithmetic assignment operators

• Character Variables• Floating Point Types• const Qualifier• Type bool• The setw Manipulator• Variable Type Summary• Type Conversion• Increment Operators• Math Library Functions

5

Main computer components

• A computer is a machine that can perform computation. a computation involves the following three components:

• Input: The user gives a set of input data.•Processing: The input data is processed by a well-defined and finite sequence of steps.•Output: Some data available from the processing step are output to the user.

Usually, computations are carried out to solve some meaningful and useful problems. One supplies some input instances for the problem, which are then analyzed in order to obtain the answers for the instances.

Why digital computers & problems types

• Usually, computer perform computations in order to solve some meaningful and useful problems faster and more accurately. One supplies some input instances for the problem, which are then analyzed in order to obtain the answers for the instances.

• Types of problems– Functional problems A set of arguments a1,a2,...,are send to Some function,

as f(a1,a2,...,an), which in turn calculate the arguments and output to the user.

– Decision problems These form a special class of functional problems whose outputs are "yes" and "no" (or "true" and "false", or "1" and "0", etc).

– Search problems Given an input object, one tries to locate some particular configuration pertaining to the object and outputs the located configuration, or "failure" if no configuration can be located.

– Optimization problems Given an object, a configuration and a criterion for goodness, one finds and reports the configuration pertaining to the object, that is best with respect to the different existing paths.

How does a program run in a computer?

• The inputs, the intermediate values and the instructions defining the processing stage reside in the (main) memory. In order to separate data from instructions the memory is divided into two parts:

• Data area The data area stores the variables needed for the processing stage. The values stored in the data area can be read, written and modified by the CPU.

• Instruction area The instruction area stores a sequence of instructions that define the steps of the program. Under the control of a clock, the computer carries out a fetch-decode-execute cycle in which instructions are fetched one-by-one from the instruction area to the CPU, decoded in the control unit and executed in the ALU. The CPU understands only a specific set of instructions. The instructions stored in memory must conform to this specification.

How does a program run in a computer?

What is programming?

• Programming is a process done by programmers to instruct a computer on how to do a task .

• It is Planning or scheduling a sequence of steps for a computer to follow to perform a task.

• Basically, telling a computer what to do and how to do it.

• A program is :

– A sequence of steps to be performed by a computer.

– Expressed in a computer language.

• Unstructured Programming • Procedural Programming • Modular & Structural Programming• Abstract Data Type• Object-Oriented Programming

• Small and (simple?) programs. • Consists only of one main

program. • Here ``main program'' stands

for a sequence of commands or statements which modify data which is global throughout the whole program.

Main Program

Data

• This programming technique can only be used in a very small program. Why?

• For example, if the same statement sequence is needed at different locations within the program, the sequence must be copied. If an error needed to be modified, every copy needs to be modified.

This has lead to the idea to extract these sequences (procedure), name them and offering a technique to call and return from these procedures.


• With procedural programming, you are able to combine sequences of calling statements into one single place.

• A procedure call is used to invoke the procedure. After the sequence is processed, flow of control proceeds right after the position where the call was made .

Main Program

Procedure

• With parameters and sub-procedures (procedures of procedures) , programs can now be written more structured and with less errors.

• For example, if a procedure is correct, every time it is used

it produces correct results.

• Consequently, in cases of errors you can narrow your search to those places which are not proven to be correct.

• Now a program can be viewed as a sequence of procedure calls.

• The main program is responsible to pass data to the individual calls, the data is processed by the procedures and the resulting data is presented.

• Thus, the flow of data can be illustrated as a hierarchical graph, a tree.

Main Program

Data

Procedure1Procedure2 Procedure3


Will be discussed next year

• Modular programming is subdividing your program into separate subprograms.

• Procedures of a common functionality are grouped together into separate modules.

• A program no longer consists of only one single part. It is now divided into several smaller parts which interact through procedure calls.

• The main program coordinates calls to procedures in separate modules and hands over appropriate data as parameters.

Main Program (Also a module)

Data

Data Data1

Module2

+Data Data2

Module1

+Data Data1

Procedure1Procedure2 Procedure3

• A subset of procedural programming that enforces a logical structure on the program being written to make it more efficient and easier to understand and modify. “organizing considering time and space”

• Certain languages such as Ada, and Pascal were designed with features that encourage or enforce a logical program

• Three Types of Structures in a structured program

-Statement sequence(s1,s2,…,sn)

-Branch(if-then-else)

-Loop(for,do, and while loops)

- Keep modules!!!

Basic structures for programming?

Programming languages classes?

Programming Languages

• There are many different programming languages, and many ways to classify them. For example,– "high-level" programming languages are languages whose

syntax is relatively close to natural language, – whereas the syntax of "low-level" languages includes

many technical references to the (0's and 1's, etc.) • C is in many ways hard to categories. Compared to assembly

language it is high-level, but it nevertheless includes many low-level facilities to directly manipulate the computer's memory.

25

high – level languages

• Are designed to be easy to read and write• Use more complicated instructions than the CPU can follow• Must be translated to zeros and ones for the CPU to execute a

program

26

Machine, Assembler and high level language

• Machine language is a numeric language specifically understood by a computer’s processor (the CPU).

• Assembly language consist of statements written with short mnemonics such as ADD, MOV, ….It has a one-to- oneone-to- one relationship with machine language instructions

• High level language ( such as C++ and Java) has a one–to–one–to–manymany relationship with machine/assembly language instructions

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How computers understand the instruction?

• Programs are written in a programming language, then translated into machine code by a compiler and linker so that the computer can execute it directly or run it line by line (interpreted) by an interpreter program.

Compilers

• Translate high-level language to machine language

LinkersA Linker combines

– The object code for the programs we writeAnd

– The object code for the pre-compiled routinesInto

– The machine language program, the CPU can run (executable program)

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Agenda

• Introduction - computer hardware & Programming Languages

• First Program• Output Using print

• Directives• Comments

• Integer Variables• Input with scanner• Variable Names• Arithmetic Expressions

• The arithmetic assignment operators

30

The First Java Program

class Welcome { /* The Welcome Program Illustrates a simple program displaying a message. */ public static void main (String [ ] args) { System.out.println("Welcome to Java!"); } // end method main} // end class welcome

Type all carefully and save it to a file named Welcome.java


class Welcome {

/* The Welcome Program Illustrates a simple program displaying a message. */ public static void main (String [ ] args) { System.out.println("Welcome to Java!"); } // end method main} // end class welcome

Java program source files (.java) contain definition of classes


class Welcome {

/* The Welcome Program Illustrates a simple program displaying a message. */ public static void main (String [ ] args) { System.out.println("Welcome to Java!"); } // end method main} // end class welcome

The class name or identifier

• class names begin with a capital letter and capitalize the first letter of each word they include (e.g., SampleClassName).

• A class name is an identifier—a series of characters consisting of letters, digits, underscores (_) and dollar signs ($) that does not begin with a digit and does not contain spaces.

• Ex. valid identifiers such as Welcome1, $value,_value, m_inputField1 and button7.

• Ex. Invalid identifiers such as 7button -not a valid identifier because start with digit input field - not a valid identifier because it contains a space

• identifier that does not begin with a capital letter is not a class name.• • Java is case sensitive—uppercase and lowercase letters are distinct—so value and Value are

different.

Class name or identifier


class Welcome {

/* The Welcome Program Illustrates a simple program displaying a message. */

public static void main (String [ ] args) { System.out.println("Welcome to Java!"); }}

Curly braces pair enclose a block of code, class Welcome here

Don’t miss me!


class Welcome {

/* The Welcome Program Illustrates a simple program displaying

a message. */


Curly braces pair enclose a block of code, method main() here

Don’t miss me!


class Welcome {


a message. */


This is a block of comments, for human, not for computer

It explains to you what happens


class Welcome {


a message. */

public static void main (String [ ] args) { System.out.println("Welcome to Java!"); } // end of method main} // end of class

/* and */ pair encloses a comment block(over several lines)

Don’t miss me!

One line comment


class Welcome {


a message. */


This is a method of the class Welcome, named main()

• The parentheses after the identifier main indicate that it’s a program building block called a method.

• Java class declarations can contain one or more methods.

• one of the methods must be called main and must be defined as shown previously otherwise, the JVM will not execute the application

Declaring a method


class Welcome {


a message. */


There MUST be a pair of parentheses following ALL method names

Don’t miss me!


class Welcome {


a message. */


A method may take some input from the caller, formally known as arguments or

parameters


class Welcome {


a message. */


A method may give some output to the caller too, known as return value

void means no return value


class Welcome {


a message. */


The static keyword before a method definition indicates this is a class method


class Welcome {

/* The Welcome Program Illustrates a simple program displaying a message. */


This method is a public one, others can call me.


class Welcome {


a message. */


Standard properties of the main() method


class Welcome {


a message. */


A statement (instruction) to display a message “standard output object”

System . Out . println(“string");

Selecting method printClass System, defined

in the Standard Package of java

Selects an individual class member of

System

Output stream object, it is member

of System

Selects an individual class member of Out

Method member of Out

Parameter of Print method


class Welcome {


a message. */


After every statement, there must be a semi-colon!


class Welcome {


a message. */


How to ask the computer to act according to the instructions in this program?

class Welcome2 {

/* The Welcome2 Program Illustrates a simple program displaying

a message. */

public static void main (String [ ] args) { System.out.print( "Welcome to " ); System.out.println( "Java Programming!" ); }}

The out put will be

Welcome to java programming

class Welcome3 {


a message. */

public static void main (String [ ] args) { System.out.print( "Welcome\nto" ); System.out.println( "Java Programming!" ); }}The out put will beWelcometo java programming

class Welcome3 {


a message. */

public static void main (String [ ] args) { System.out.printf("%s\n%s\n", "Welcome to", "Java Programming!"); }}

The outputWelcome toJava Programming!

Displaying Text with printfDisplaying Text with printfFormat pacifiers begin

with %

Place holder for sting

• Creating a program.• Compiling a Java program into byte codes.• Loading program into memory.• Byte code verification.• Execution.

What do we do with it?Java program has five steps to be executed

• consists of editing a file with an editor program.

• Type a Java program (typically referred to as source code) using the editor, Use any text editor you like (preferred IDEs environment)

• Make any necessary corrections and save the program on a secondary storage device, such as your hard drive. save as Welcome.java

• A file name ending with the .java extension indicates that the file contains the Java source code.

Creating a program

• is a software application that provides comprehensive facilities to computer programmers for software development.

• An IDE normally consists of:– a source code editor – build automation tools – a debugger

• Some IDEs contain compiler, interpreter, or both, such as Eclipse; others do not,

• An easy way to find where the compiler thinks you’ve gone wrong• Examples: NetBeans, Eclipse, Together,…

Integrated Development Environments (IDEs)

• use the command javac (the Java compiler) to compile a program.

• For example, to compile a program called Welcome.java, you’d type in the command prompet javac Welcome.java

• the compiler produces a .class file called Welcome.class that contains the compiled version of the program.

• The Java compiler translates Java source code into bytecodes that represent the tasks to be executed.

• Bytecodes are executed by the Java Virtual Machine (JVM)—a part of the JDK and the foundation of the Java platform.

• The JVM is one of the most widely used virtual machines that its execution can be used on all those platforms.

• JVM is unlike machine language, which is dependent on specific computer hardware, bytecodes are platform independent

Compiling a Java program into byte codes

• the JVM places the program in memory to execute it—this is known as loading.

• The JVM’s class loader takes the .class files containing the program’s bytecodes and transfers them to primary memory.

Loading program into memory

• as the classes are loaded, the bytecode verifier examines their bytecodes to ensure that they’re valid and do not violate Java’s security restrictions

Byte code verification

• the JVM executes the program’s bytecodes, thus performing the actions specified by the program.

• In early Java versions, the JVM was simply an interpreter for Java bytecodes. This caused most Java programs to execute slowly, because the JVM would interpret and execute one bytecode at a time.

• Some modern computer architectures can execute several instructions in parallel.

Execution/Running.

• Editing– Use any text editor you like (not a word processor!); save

as Welcome.java• Compiling

– From a DOS or UNIX command line, type> javac Welcome.java

– This should produce the file Welcome.class• Running/Executing

– Again from the command prompt, type> java Welcome

What do we do with it?

• That Java programs actually go through two compilation phases—– one in which source code is translated into bytecodes (for portability across

JVMs on different computer platforms) and – a second in which, during execution, the bytecodes are translated into

machine language for the actual computer on which the program executes.

• Problems That May Occur at Execution Time : divide by zero

Note

Test your self

• What will be the out put of the following code:-public class FormattingExample

{

public static void main (String [] args)

{

System.out.print("lol\tz\n");

System.out.println("hello\rworld");

System.out.println("\"Geek\" talk slash (\\) com");

}

}

64

solution

• The output will beLol zhelloworld"Geek" talk slash (\) com

65

• 1-The programs that translate high-level language programs into machine language are called ____________.

• 2-The command _______from the JDK executes a Java application.

• 3-The command ______from the JDK compiles a Java program.

• 4-A Java program file must end with the file extension______.

• 5-When a Java program is compiled, the file produced by the compiler ends with the file extension________.

• 6-The file produced by the Java compiler contains _____that are executed by the Java Virtual Machine.

Questions (your turn)

• 12- What is the out put of the following code:class Display {

/* The Display Program Illustrates a simple program displaying

a message. */

public static void main (String [ ] args) { System.out.print( “Now is autumn " ); System.out.println( “weather is not stable" ); System.out.print( “sometimes hot " ); System.out.println( “sometimes cold" ); }}

Your turn …. Cont.

• 1- compilers.• 2- java (file name).• 3- javac (file name).• 4-(file name).java.• 5- (file name).class.• 6- bytecodes.• 12- Now is autumn weather is not stable sometimes hot sometimes called

Answers

• Design a program to output the following table on the screen. Not you must use the escape sequence.

Person height shoe size===========================Ahmed 1.7 m 38Ali 2 m 43

Self study program

solution

public static void main(String[] args) { System.out.println("person\t heiht\t size"); System.out.println("======================"); System.out.println("Ahmed\t1.7m\t38"); System.out.println("Ali\t2m\t43");}

70

Agenda

• Introduction - Programming Languages• First Program

• Output • Directives• Comments

• variables & identifiers• Integer Variables• Input with scanner• Variable Names• Arithmetic Expressions

• The arithmetic assignment operators71

Variables & Identifiers

• programming is not limited only to printing simple texts on the screen. In order to go a little further on and to become able to write programs that perform useful tasks that really save us work we need to introduce the concept of variable.

• we can define a variable as a portion of memory to store a determined value.

• Each variable needs an identifier that distinguishes it from the others

Variable Names=identifier

• The names given to variables are called identifiers. • What are the rules for writing identifiers?

– You can use upper- and lowercase letters, and the digits from 1 to 9.

– You can also use the underscore _. – The first character must be a letter or underscore.– Keywords is avoided.

• Identifiers can be as long as you like, but most compilers will only recognize the first few hundred characters.

• java is case sensitive: The compiler distinguishes between upper- and lowercase letters, so Var is not the same as var or VAR.

73

keyword• A keyword is a predefined word with a special meaning.• int, class, if, and while are examples of keywords. • A complete list of keywords can be found in Appendix B, page

886, book “object oriented programming in C++”.

• Note:• Declarations of variables can be placed almost anywhere in a

program, but they must appear before their corresponding variables are used in the program.

74

Java Keywords

abstract boolean break byte case catch char

class const continue default do double else

extends final finally float for goto if

implements import instanceof int interface long native

new package private protected public return short

static super switch synchronized this throw throws

transient try void volatile while

Declaring Variables: Syntax

• Format:<type of information> <name of variable>;

• Example:char a;

• Variables can be initialized (set to a starting value) as they’re declared:char myFirstInitial = ‘j’;

int age = 30;

Some Built-In Types Of Variables In Java

Type Description

byte 8 bit signed integer

short 16 but signed integer

int 32 bit signed integer

long 64 bit signed integer

float 32 bit signed real number

double 64 bit signed real number

char 16 bit Unicode character (ASCII and beyond)

boolean 1 bit true or false value

String A sequence of characters between double quotes ("")

Location Of Variable Declarations

public class <name of class>

{

public static void main (String[] args)

{

// Local variable declarations occur here

<< Program statements >>

: :

}

}

Style Hint: Initializing Variables

• Always initialize your variables prior to using them!– Do this whether it is syntactically required or not.

• Example how not to approach:

public class OutputExample1

{

public static void main (String [] args)

{

int num;

System.out.print(num);

}

} OutputExample1.java:7: error: variable num might not have been initialized System.out.print(num); ^

Java Constants

Reminder: constants are like variables in that they have a name and store a certain type of information but unlike variables they CANNOT change.

Format: final <constant type> <CONSTANT NAME> = <value>;

Example: final int SIZE = 100;

Location Of Constant Declarations

public class <name of class>{ public static void main (String[] args) {

// Local constant declarations occur here (more later)// Local variable declarations

< Program statements >> : :

} }

Why Use Constants?

1. They make your program easier to read and understand

populationChange = (0.1758 – 0.1257) * currentPopulation;

Vs.

final float BIRTH_RATE = 17.58;

final float MORTALITY_RATE = 0.1257;

int currentPopulation = 1000000;

populationChange = (BIRTH_RATE - MORTALITY_RATE) * currentPopulation;

Variables, cont.

int -- integer type: range is system dependent usually 32-bits -- +/- 2,147,483,648 16-bits on older systems -- +/- 32,768

float -- floating point number char -- a single character string -- more than an array of characters (a class)

we’ll look at these in more detail later..

83

Common Java Operators / Operator Precedence

Precedence level

Operator Description Associativity

1 expression++

expression--

Post-increment

Post-decrement

Right to left

2 ++expression

--expression

+

-

!

~

(type)

Pre-increment

Pre-decrement

Unary plus

Unary minus

Logical negation

Bitwise complement

Cast

Right to left


Precedence level


3 *

/

%

Multiplication

Division

Remainder/modulus

Left to right

4 +

-

Addition or String concatenation

Subtraction

Left to right

5 <<

>>

Left bitwise shift

Right bitwise shift

Left to right


Precedence level


6 <

<=

>

>=

Less than

Less than, equal to

Greater than

Greater than, equal to

Left to right

7 = =

!=

Equal to

Not equal to

Left to right

8 & Bitwise AND Left to right

9 ^ Bitwise exclusive OR Left to right


Precedence level


10 | Bitwise OR Left to right

11 && Logical AND Left to right

12 || Logical OR Left to right


Precedence level


13 =

+=

-=

*=

/=

%=

&=

^=

|=

<<=

>>=

Assignment

Add, assignment

Subtract, assignment

Multiply, assignment

Division, assignment

Remainder, assignment

Bitwise AND, assignment

Bitwise XOR, assignment

Bitwise OR, assignment

Left shift, assignment

Right shift, assignment

Right to left

Example

89

Arithmetic Operators, cont.

• There is no arithmetic operator for exponentiation in Java, so x2 is represented as x*x.

90

The arithmetic assignment operatorspublic static void main(String[ ] args) {

int j = 0,k = 5;

k = k - 5;

}

The same variable may appear on both sides of an assignment operator on the right hand side of the assignment operator, the variable in

question represents its value prior to the execution of this statement.

on the left hand side of the assignment operator, the variable receives a new value which is the result of the evaluation on the right hand side.

In our example above, k ends up being “0”.

91

The arithmetic assignment operators, cont.

public static void main(String[] args)

{ int j = 0,k = 5;

k -= 5; // really like k = k - 5;

}

When performing any other operation on a variable and stuffing the value back into the same variable, use a shortcut (like +=, -=, *=, %=)

92

The arithmetic assignment operators, cont.

93

Post/Pre Operators

The name of the online example is: Order1.java

public class Order1{ public static void main (String [] args) { int num = 5; System.out.println(num); num++; System.out.println(num); ++num; System.out.println(num); System.out.println(++num); System.out.println(num++); }}

Post/Pre Operators (2)

The name of the online example is: Order2.java

public class Order2{ public static void main (String [] args) { int num1; int num2; num1 = 5; num2 = ++num1 * num1++; System.out.println("num1=" + num1); System.out.println("num2=" + num2); }}

Unary Operator/Order/Associativity

The name of the online example: Unary_Order3.java

public class Unary_Order3.java{ public static void main (String [] args) { int num = 5; float fl; System.out.println(num); num = num * -num; System.out.println(num); }}

Accessing Pre-Created Java Libraries

• It’s accomplished by placing an ‘import’ of the appropriate library at the top of your program.

• Syntax:import <Full library name>;

• Example:import java.util.Scanner;

Getting Text Input

• You can use the pre-written methods (functions) in the Scanner class.

• General structure:import java.util.Scanner;

main (String [] args){ Scanner <name of scanner> = new Scanner (System.in); <variable> = <name of scanner> .<method> (); }

Creating a scanner object (something that can scan user input)

Using the capability of the scanner object (actually getting user input)

Getting Text Input (2)

The name of the online example: MyInput.java

import java.util.Scanner;

public class MyInput{ public static void main (String [] args) { String str1; int num1; Scanner input = new Scanner (System.in); System.out.print ("Type in an integer: "); num1 = in.nextInt (); System.out.print ("Type in a line: "); in.nextLine (); str1 = input.nextLine (); System.out.println ("num1:" +num1 +"\t str1:" + str1); }}

Useful Methods Of Class Scanner1

• nextInt ()• nextLong ()• nextFloat ()• nextDouble ()• nextLine ();

Reading A Single Character

• Text menu driven programs may require this capability.• Example:

GAME OPTIONS

(a)dd a new player

(l)oad a saved game

(s)ave game

(q)uit game

• There’s different ways of handling this problem but one approach is to extract the first character from the string.

• Partial example:String s = "boo“;

System.out.println(s.charAt(0));

Reading A Single Character

• Name of the (more complete example): MyInputChar.java

import java.util.Scanner;public class MyInputChar{ public static void main (String [] args) { final int FIRST = 0; String selection; Scanner input = new Scanner (System.in); System.out.println("GAME OPTIONS"); System.out.println("(a)dd a new player"); System.out.println("(l)oad a saved game"); System.out.println("(s)ave game"); System.out.println("(q)uit game"); System.out.print("Enter your selection: ");

Reading A Single Character (2)

selection = in.nextLine ();

System.out.println ("Selection: " + selection.charAt(FIRST));

}

}

The best way to learn a programming language is to try writing programs

and test them on a computer

104

Your Turn

• 1. Dividing a program into functionsa. is the key to object-oriented programming.b. makes the program easier to conceptualize.c. may reduce the size of the program.d. makes the program run faster.

• 2. A function name must be followed by ________.• 3. A function body is delimited by ________.• 4. Why is the main() function special?• 5. A C++ instruction that tells the computer to do something is

called a ________.

105

Your Turn, cont.

• 9. True or false: A variable of type char can hold the value 301.

• 10. What kind of program elements are the following?a. 12b. ‘a’c. 4.28915d. JungleJime. JungleJim()

106

Your Turn, cont.

• 11. Write statements that display on the screena. the character ‘x’b. the name Jimc. the number 509

• 12. True or false: In an assignment statement, the value on the left of the equal sign is always equal to the value on the right.

• 15. Write a statement that gets a numerical value from the keyboard and places it in the variable temp.

107

Your Turn, cont.

• 19. The expression 11%3 evaluates to ________.

• 21. Write a statement that uses an arithmetic assignment operator to increase the value of the variable temp by 23. Write the same statement without the arithmetic assignment operator.

• 22. write a program in order to ask the user about the number of programming language he had before, the out the statement “enjoy the book” to the screen?

108

• 23- Write a program which asks the user to insert two integer values then out put on the screen– The incrementing by one to each intergers.– The multiplication of both;– The adding of both numbers.

Answers• 1- b,c.• 2-parentheses• 3- braces { }• 4- It’s the first function executed when the program starts• 5- statement• 9- false• 10- a. integer constant

– b. character constant– c. floating-point constant– d. variable name or identifier– e. function name

• 11. – a. cout << ‘x’;– b. cout << “Jim”;– c. cout << 509;

• 12- false; they’re not equal until the statement is executed• 15- cin >> temp;• 19- 2• 21-

– temp += 23;– temp = temp + 23;

• 22- #include <iostream>• using namespace std;• int main( )• {• int numberOfLanguages;• cout << "Hello reader.\n“ << "Welcome to C++.\n";• cout << "How many programming languages have you used? ";• cin >> numberOfLanguages;• cout << "Enjoy the book.\n";• return 0; }

• 22. #include <iostream>• using namespace std;• int main(){• int n,m;• cout<<"enter the first number\n";• cin>>n;• cout<<"enter the second number\n";• cin>>m;• n++; m++;• cout<<"the first number after increment is "<<n<<endl;• cout<<"the second number after increment is "<<m << endl;• n--; m--;• cout<< "the multiplication of the two integers are"<<m*n<<endl; • cout<< "the addition of the two integers are"<<m+n<<endl; }

Lecture 3Agenda

• Text book “absolute C++”• Chapter1:C++ basics cont.

– Variable types• Char, string, float, const, boolean.

– Type conversion– Math operations

• Chapter 2: flow of control– Boolean expression.– Branching mechanisms.– Loops.– Introduction to file input.

Character variable// charvars.cpp// demonstrates character variables• #include <iostream> //for cout, etc.• using namespace std;• int main()• {• char charvar1='A'; //define char variable as character• char charvar2='\t'; //define char variable as tab• cout << charvar1; //display character• cout << charvar2; //display character• cout << charvar1; //display character• cout << "\n"; //display newline character• return 0;• }

Character variable : Escape Sequences

• \ xdd Hexadecimal notation• Sometimes you need to represent a character

constant that doesn’t appear on the keyboard, such as the graphics characters above ASCII code 127.

• To do this, you can use the “\xdd” “\xdd” representation,• where each dd stands for a hexadecimal digithexadecimal digit.

• cout << “\xE0”; //display α cout << “\xB2”; //display solid rectangle

ASCII Table

String variable

• In order to use string variable type, we have to use special library called “String”.

Cin>> with string variable type

String variable• #include <iostream>• #include <String> //using string variable• using namespace std;• int main()• {• string strname; // identify a string variable• cout<<" enter your name"<< endl;• cin>>strname;• cout<<"you typed the name"<<strname<<endl;• return 0;• }

Floating Point Types• represent numbers with a decimal place—like 3.1415927, 0.0000625, and

–10.2.• There are three kinds of floating-point variables in C++:

– type float, – type double, – and type long double

• float PI = 3.14159F; //the F specifies that it’s type float• You can also write floating-point constants using exponential notationexponential notation. • Exponential notation is a way of writing large numbers without having to

write out a lot of zeros. • For example:

– 1,000,000,000 can be written as 1.0E9 in exponential notation.– 6.35239E–5 is equivalent to 0.0000635239 in decimal notation

The const Qualifier120

• The keyword const (for constant) precedes the data type of a variable.

• It specifies that the value of a variable will not change throughout the program.

• Any attempt to alter the value of a variable defined with this qualifier will elicit an error message from the compiler.

• const float PI = 3.14159F; //type const float

Example: circarea.cpp121

// circarea.cpp// demonstrates floating point variables#include <iostream> //for cout, etc.using namespace std;int main(){float rad; //variable of type floatconst float PI = 3.14159F; //type const floatcout << "Enter radius of circle: "; //promptcin >> rad; //get radiusfloat area = PI * rad * rad; //find areacout << "Area is " << area << endl; //display answerreturn 0;}

Type bool122

• Variables of type bool can have only two possible values: true and false.

• type bool is most commonly used to hold the results of comparisons.

Basic C++ Variable Types123

Type Conversion124

• C++ treats expressions involving several different data types.

int main(){int count = 7;float avgWeight = 155.5F;double totalWeight = count * avgWeight;cout << “totalWeight=” << totalWeight << endl;return 0;}

Type Conversion, cont.125

• When two operands of different types are encountered in the same expression, the lower-type variable is converted to the type of the higher-type variable.


int count = 7;float avgWeight = 155.5F;double totalWeight = count * avgWeight;

• the int value of count is converted to type float and stored in a temporary variable before being multiplied by the float variable avgWeight.

• The result (still of type float) is then converted to double so that it can be assigned to the double variable totalWeight.


Type Conversion, cont.

Casts128

• Cast convert a value from one type to another.

• CharVar = static_cast<char>(nIntVar);

• Example:cout<< static_cast<int>('A'); // print ‘A’ as integer , 65

cout<< static_cast<char>(65); // print 65 as ‘A’

Increment and Decrement Operators, cont.


• When you increment (++) or decrement (--) a variable in a statement by itself, the pre-increment and post-increment forms have the same effect, and the pre-decrement and post-decrement forms have the same effect.

X++;++X;

• It’s only when a variable appears in the context of a larger expression that pre-incrementing the variable and post-incrementing the variable have different effects (and similarly for pre-decrementing and post-decrementing).

• The Next slide shows the precedence and associatively of the operators introduced to this point.


The precedence of the operators131

Increment and Decrement Operators, cont.132

• totalWeight = avgWeight * ++count;count is incremented first and then multiply

with avgWeight

• totalWeight = avgWeight * count ++;the multiplication would have been performed

first, then count would have been incremented.

Increment and Decrement Operators, cont.133

Math Library Function134

// sqrt.cpp // demonstrates sqrt() library function#include <iostream> //for cout, etc.#include <math.h> <math.h> //for sqrt()using namespace std;int main(){double number, answer; //sqrt() requires type doublecout << “Enter a number: “;cin >> number; //get the numberanswer = sqrt(number); //find square rootcout << “Square root is “ << answer << endl; //display itreturn 0;}Enter a number: 1000Square root is 31.622777

Math Library Function, cont. 135

Math Library Function, cont.136

Outlines

• Chapter 2 – flow of controlChapter 2 – flow of control– Boolean expressions– Branching mechanisms– Loops– Decisions

137

Control Structures138

• Normally, statements in a program execute one after the other in the order in which they’re written.– Called sequential execution.

• Various C++ statements enable you to specify that the next statement to execute may be other than the next one in sequence.– Called transfer of control.

• All programs could be written in terms of only three control structures– the sequence structure– the selection structure and – the repetition structure

Boolean expressions139• Most branching statements are controlled by Boolean expressions.

• A Boolean expression is any expression that is either true or false. • The simplest form for a Boolean expression consists of two expressions, such

as numbers or variables, which are compared with one of the comparison operators as shown.

Building Boolean Expressions• One can combine two comparisons in order to build a

Boolean expression. – Ex. (2 < x) && (x < 7).– It means that the expression is true if x is greater than 2

and x is less than 7.• When two comparisons are connected using an && , the

entire expression is true, if both of the comparisons are true; otherwise, the entire expression is false.– Ex. (y < 0)||(y < 12)

• When two comparisons are connected using a || , the entire expression is true provided that one or both of the comparisons are true; otherwise, the entire expression is false.

Evaluating Boolean Expressions141

• #include <iostream> //for cout, etc.• using namespace std;

int main(){ int y; bool Opor, Opand;cout<<"enter number";cin>>y;Opor=(y<7)||(y>2);cout<<"the result of the or operator is\n"<<Opor<<endl;Opand=Opor=(y<7)&&(y>2);cout<<"the result of the and operator is \n"<<Opand;return 0;}

• C++ compiler considers that a true expression true expression has the value 1value 1, while a false expression false expression has the value 0value 0.

Evaluating Boolean Expressions cont.142

Precedence Rules143 • Boolean expressions (and arithmetic expressions) need not be

fully parenthesized.• If you omit parentheses, the default precedence will be used.

High precedence

low precedence

Some expressions that use Boolean expression144

• int x= 44; //assignment statement• int y = 12; //assignment statement• bool b1= (x== y); //false• bool b2=(y <= 12); //true• bool b3=(x> y); //true• bool b4=(x>= 44); //true• bool b5=(y != 12); // false• bool b6=(7 < y); //true• bool b7=(0); //false (by definition)• bool b8=(44); //true (since it’s not 0)

• Although C++ generates a 1 to indicate true, it assumes that any value other than any value other than 0 (such as –7 or 44) is true0 (such as –7 or 44) is true; only 0 is falseonly 0 is false.

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