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Lesson # 1

By : Doa'a M Bamasoud

computer science student 

 

White Color: Titles,Adresses,Me...etc    

Pink Color : My Comments      

Red Color : Concentrate , Must Have Your Attention    

Yellow Color : Commands , Output , Braces , Functions ..etc 

 

 

1-1 Introduction


This lesson is a quick tutorial on C Programming language.
I assume that you are familiar with at least one of famous
operating systems.

You can use the following compilers or
Programming Environments.

- cc in Unix or gcc in Linux operating systems
- Borland C or Turbo C in DOS operating system
- Visual C++ (create a simple win32 console
       application.) in Windows
- C++Builder (create a console application using
       console app wizard) in windows

I suggest a simple environment like Unix, Linux or DOS.
Windows compilers are very complex for newbie programmers.



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1-2 Your first C program


Let's write our first C program.

#include <stdio.h>
main()
{
printf
("Hello World!\n");
}

First step for running this program is to make a text file
containing above code. Be sure that the file is a pure text
file. You must save the text file with .c extension.

Then you must compile the source code. The result of compile
step is an executable file that you can run it.

To compile program under Unix operating system use the
command:

$ cc test.c

and under linux type

$ gcc test.c

The resulting executable file is a.out file. To run this
executable you must type:

$./a.out

Program output must appear on your screen.

Hello World!

To compile the source code in other environments, you must
use their Development Environment. You must consult your
compiler User's Guide for this.



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1-3 Details of Test program


#include <stdio.h>
Tells C compiler to include the file "stdio.h" in this point
of your C program before starting compile step. This
"include file" contains several definitions , declerations
etc.

main()
C program consist of one or more functions. Functions are
building blocks of C programs. main() function is different
from other functions by that it is the start point of
program execution. Our program contains only function while
complicated programs may contain thousands.

{ Opening brace marks the start of a block. Closing brace
will mark its end. This one marks main () function start

printf("Hello world!");
This line of code prints the statement between quotation
marks on your output screen. \n tells program to start a
new line in output screen.

Each command line in C ends with ";" character. Control
statements are exceptions. You will soon be able to
determine when you must use ; to end a line of code.

} closes main() function.
This program contains only one function while complicated
programs may contain several functions.

------------------------------------------------------------


1-4 Data types and variables


C uses several data types of data. These include characters,
integer numbers and float numbers.

In C language you must declare a variable before you can use
it.

Declaring a variable to be an integer or a character for
example will let computer to allocate memory space for
storing and interpreting data properly.

------------------------------------------------------------


1-5 Naming a variable


It's better that you use meaningful names for your variables
even if this causes them to became long names. Also take this
in mind that C is case sensitive. A variable named "COUNTER"
is different from a variable named "counter".

Functions and commands are all case sensitive in C Programming
language. You can use letters, digits and underscore _
character to make your variable names. Variable names can be
up to 31 characters in ANSI C language.

The declaration of variables must take place just after the
opening brace of a block. For example we can declare variables
for main() function as below code:

main()
{
int
count;
float sum,area;
..
..
..
}

First character in a variable name must be a letter or an
underscore character. It cannot be a C programming
language-reserved word (i.e. Commands and pre defined
function names etc)

An example for using variables comes below:

#include<stdio.h>
main()
{
int
sum;
sum=12;
sum=sum+5;
printf("Sum is %d",sum);
}

General form for declaring a variable is:

     Type  name;

The line sum=sum+5; means: Increase value of sum by 5.
We can also write this as sum+=5; in C programming language.

printf function will print the following:
Sum is 17

In fact %d is the placeholder for integer variable value
that it's name comes after double quotes.


Common data types are:
int              integer
long    long integer
float    float number
double      long float
char         character


Other placeholders are:

%d    decimal integer
%ld   decimal long integer
%s    string or character array
%f    float number
%e    double ( long float)


printf () function used in this example contains two sections.
First section is a string enclosed in double quotes. It is
called a format string. It determines output format for
printf function. Second section is "variable list" section.

We include placeholders for each variable listed in variable
list to determine it's output place in final output text of
printf function.

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1-6 Control characters


As you saw in previous examples \n control character makes a
new line in output. Other control characters are:

\n New line
\t  tab
\r carriage return
\f form feed
\v vertical tab

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1-7 Multiple functions

Look at this example:

#include<stdio.h>
main()
{

printf("I am going inside test function now\n");

test();
printf("\nNow I am back from test function\n");
}


/* be careful am now out side the main function and am going to get into the test func. */


test()
{

int a,b;
a=1;
b=a+100;
printf("a is %d and b is %d",a,b);
}

In this example we have written an additional function. We
have called this function from inside main function. When we
call the function, program continues inside test () function
and after it reached end of it, control returns just after
test () function call in main ()

You see declaring a function and calling it, is an easy task.

Just pay attention that we used ";" when we called the function
but not when we were declaring it.

I finished this lesson here. Now try to do lesson exercises
and know the point that you will not learn anything if you do
not do programming exercises.



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Exercises

------------------------------------------------------------
You can send your solutions for the exercises to the following E-mail address :

doaanos@bonbon.net


------


Exercise 1: What is the exact output result of this code.

#include <stdio.h>

main()
{

printf("Hi\nthere\nWhat is the output\n?");
}


Exercise 2: Write a program that declares two floating
numbers. Initialize them with float values. Then print
their sum and multiplication in two separate lines.

Exersise 3 :Write the output result of multiple function
example in this lesson.

Exercise 4: Why these variable names are not valid ?

test$var
my counter
9count
float

 

DOA'A  M  BAMASOUD

computer science student