CMPT 128: Introduction to Computing Science for Engineering Students

© Janice Regan, CMPT 128, Jan 2007 1

CMPT 128: Introduction to Computing Science for Engineering Students

Introduction to the basic components ofC and C++ programs

Janice Regan CMPT 128 2007-2012 2

Introduction Computer program: an ordered sequence of

instructions whose objective is to accomplish a task.

Programming: process of planning and creating a program

Programming Language: a set of symbols, special words (semantics), and rules for using those symbols and special words (syntax) to create statements to implement the ordered sequence of instructions to accomplish a task


Problem solving When we try to solve a problem using

programming we should always begin by breaking the problem into parts. Each part describes a process that solves

part of the problem (or an object that is part of the problem)

Each part can be implemented as a function within a program to solve the problem (or a class)


Programs and Libraries Programs are divided into smaller

modules called functions. Functions can

be separately tested and reused by many programs

Use other functions Be used by other functions Become part of libraries


Programs Every program has a main function.

The main function controls the highest level of abstraction of the program.

The main function may call other functions to complete lower level tasks (like evaluating an exponential)

Many commonly needed functions are supplied in libraries as part of the C and or C++ language, some less commonly needed functions are available as additional add on libraries

C and C++ C is a subset of C++

C codes will run inside a C++ application All C libraries are available in C++

C++ contains many extensions of C C++ is object oriented and allows classes C++ libraries that are based on classes

cannot be used in C

© Janice Regan, CMPT 128, Sept 2007 6


The Components of a Program Each C or C++ program includes a series of

functions or program units. Every C or C++ application program includes a main

function, sometimes called a main program There may be other functions used by the main

program. Functions from C libraries and C++ libraries (for C++ programs only)

Functions written by the user

For your first programs we will illustrate only a main function and some functions from libraries


Hello World: your first C++ program

// My first C++ program // make the computer print Hello world

// connect to any necessary libraries or objects#include <iostream>

// required, will be explained later in the courseusing namespace std;

// the main function, implements the algorithm to solve the problem// the main function may use functions // main uses input an output functions from the iostream class (library). cout is one of these functions. int main ( ) { cout << "Hello, world!“ << endl;

return 0; }


Hello World: your first C program/* My first C program */ /* make the computer print Hello world */

/* connect to any necessary libraries */#include <stdio.h>

/* the main function, implements the algorithm to solve the problem the main function may use functions input an output functions from the stdio library. printf is one of these functions. */

int main ( ) { printf( “Hello World \n” );

return 0; }


Comments Comments are essential to clearly explain the

purpose of your code and the methods of implementation used When you use another programmer’s code When another programmer tries to use your code When you try to use your own code after months or

years Comments make it is much easier to figure out

how things work in existing code. Comments are not “executed”


Good Comments Give ADDITIONAL information not

obvious from the code// This program calculates the first 20

primes…

Do not translate code into English// Add A to B (BAD COMMENT)C = A+B


C++ Comments: syntax Comments begin // and end at the end of

the line Comments can appear on their own line

// This is a comment Comments can appear on the same line as

an expression A = b + c; // b and c are numbers of people

C and C++, self documenting? A = b + c; // b and c are numbers of people

Better to writeTotalStudents = FullTimeStudents + OtherStudents;

Code is more readable when variables used have names that describe what they contain (much more later)



Hello World: your first program

// My first C++ program // make the computer print the string “Hello world”

// connect to any necessary libraries #include <iostream> using namespace std;

// the main function, implements the algorithm to solve the problem// the main function may use functions from included libraries int main ( ) { cout << "Hello, world!“ << endl; // Prints Hello world

return 0; }


C Comments: syntax Comments begin /* and end */ Comments can appear on their own line or

on their own block of lines /* This is a C comment

it continues until it is closed */ Comments can appear on the same line as

an expression A = b + c; /* add b to c, put the result in A */






return 0; }


Libraries / C++ objects A main function, or any other function may

wish to use functions in the built in libraries of the C or C++ language or in user developed or application libraries

To use such functions our program must indicate that the libraries are being used and provide a way to access those functions


Hello World: C++// My first C++ program // make the computer print the string “Hello world”

// connect to any necessary libraries or objects#include <iostream> // iostream is a stream object used to read/write using namespace std;

// the main function, implements the algorithm to solve the problem// the main function may use functions from included libraries // the iostream stream object includes read and write functions like cout int main ( ) { cout << "Hello, world!“ << endl; // Prints Hello world

return 0; }

Important In our first C++ program we are using the

iostream stream object (library). This object is used to read from the keyboard

and write to the screen Any C++ program that reads or writes

information should include the iostream stream object

Later we will look at the details of what we can do with iostream. (much more)







return 0; }

Important In our first C program we are using the stdio

library. This library is used to read from the keyboard

and write to the screen Any C program must use the stdio library Any C++ program may use either the stdio

library or the iostream class



Standard C Libraries #include <stdio.h>

The # at the beginning of the line indicates that the command is for the C preprocessor (a preprocessor directive)

The C preprocessor puts the contents of the file stdio.h into your program (function descriptions) instead of the line of code above then passes the resulting code to the compiler

If the preprocessor directive to include the library is not part of your program, your program will not be able to use the functions in the library


Standard C++ Libraries and objects #include <iostream>

The # at the beginning of the line indicates that the command is for the C preprocessor (a preprocessor directive)

The C preprocessor puts the prototypes (function descriptions) for the functions in the library or object into your program instead of the line of code above then passes the resulting code to the compiler

If the preprocessor directive to include the library is not part of your program, your program will not be able to use the functions in the library


Using Libraries in C and C++ A C or C++ program that wants to use libraries

starts with one or more include directives #include <Library_Reference> #include “Library_Reference” //(details later)

Here Library_Reference indicates the name of a file containing a list of all the functions in the library.


Syntax of include directive#include <Library_Reference>#include “Library_Reference”

“ “ indicates that the files location should be completely specified by the programmer.

< > indicates that the file is part of the C or C++ language itself and can be located by the preprocessor, compiler and linker without programmer intervention.



// connect to any necessary libraries and objects#include <iostream> // iostream is a stream object used to read and write using namespace std; // not needed for C

// the main function, implements the algorithm to solve the problem// the main function may use functions from included libraries // the iostream object includes read and write functions like cout int main ( ) { cout << "Hello, world!“ << endl; // Prints Hello world }

Name Spaces, C++using namespace std Indicates you wish to use the standard

namespace In large advanced programs it is possible that

you want to use additional namespaces to prevent naming conflicts.

For this course you will always use the standard namespace and you will always have this line in your C++ programs




// connect to any necessary libraries and objects#include <iostream> // iostream is a object used to read and write using namespace std;

// the main function, implements the algorithm to solve the problem// the main function may use functions from included libraries // the iostream object includes read and write functions like cout int main ( ) { cout << "Hello, world!“ << endl; // Prints Hello world

return 0; }






return 0; }


Creating a C or C++ main function

int main ( ) { /* Body of the main function */

return 0; }

The start of the main method is indicated by the statementint main ( )

The body of the main method (the code that accomplishes the task of the main function) is enclosed in { }.

The convention used in this course in to put each of the { } on a separate line.



// connect to any necessary libraries and objects#include <iostream> // iostream is an object used to read and write using namespace std;

// the main function, implements the algorithm to solve the problem// the main function may use functions from included libraries // the iostream object includes read and write functions like cout int main ( ) { cout << "Hello, world!“ << endl; // Prints Hello world return 0; }

Body of the C++ program For our first program the body consists of

a single line of codecout << "Hello, world!“ << endl;

cout prints to the screen Everything inside the “ “ is printed endl means move to the start of the next

line before printing anything else


Simple examples of C++ cout Print the word OUCH to the screen

cout << “OUCH”; Move to the beginning of a new line then

print the sum of 6.5 and 3.5 to the screen cout << endl << 6.5 + 3.5; Prints lines below to the screen

OUCH10


Simple examples of C++ cout Print the word OUCH to the screen

cout << “OUCH”; Move to the beginning of a new line then

print the sum of 6.5 and 3.5 to the screen float result; // create a variable result

…result = 6.5 + 3.5;cout << endl << result;


What is printedcout << “OUCH”;cout << endl << 6.5 + 3.5;

ANDint result = 0;cout << “OUCH”;;result = 6.5 + 3.5;cout << endl << result;

BOTH Print the lines below to the screenOUCH10







return 0; }

Body of the C program For our first program the body consists of

a single line of codeprintf( “Hello World \n” );

printf prints to the screen Everything inside the “ “ is printed except

control characters preceded by \ \n means move to the start of the next

line before printing anything elseJanice Regan CMPT 128 2007-2012 37

Simple examples of C printf Print the word OUCH to the screen

printf( “OUCH”); Move to the beginning of a new line then

print the sum of 6.5 and 3.5 to the screen printf( “\n %lf”, 6.5 + 3.5);


Simple examples of C printf Print the word OUCH to the screen

printf( “OUCH”); Move to the beginning of a new line then

print the sum of 6.5 and 3.5 to the screen float result; // create a variable result

…result = 6.5+3.5;printf( “\n %f”, result);


What about return(0) We will discuss the details of what return

means when we discuss functions and testing in more detail

For now, return(0); is how we indicate a place in the program where execution ends. Can there be more than one return(0) in one

program?


Documents

CMPT 128: Introduction to Computing Science for Engineering Students