Structure of a C Program

C Programming

A program written in C is really not much more difficult to understand than one written in any other language. once you have have gotten used to the syntax. Learning C is largely a matter of practice.

Let's investigate the various elements of a simple C program;

void main (void)

{

printf("Jamil Murad Baloch");

}

Function Definition

All C programs are divided into units called "functions". main() is a function. Every C program consists of one or more functions. main () is the one to which control is passed from the operating system when the program is run. The word void preceding main specifies that the function main() will not return a value, the second void in parenthesis specifies that the function takes no arguments.

Delimiters

following the function definition are braces which signal the beginning and end of the body of the function. The opening brace { indicates that a block of code that forms a distinct unit is about to begin and the closing brace } terminates the block of code.

Statement Terminator

The line in our program that begins with the word "printf" is an example of a statement. A statement in C is terminated with a semicolon.

The Printf ( ) Function

the program statement

printf("Jamil Murad Baloch");

causes the phrase in quotes to be printed on the screen. the word printf is actually a function name, just as "main" is a function name. 

Exploring the printf( ) function

Printing numbers

The printf ( ) function uses a unique format for printing constant and variables. let's look at an example:

void main ( )

{

printf ("This is the number five: %d",5);

}

The printf ( ) can be given more than one argument. In this example we gave it two arguments: ("This is the number five: %d") on the left and a value (5) on the right. These two arguments are separated by a coma.

Format Specifiers

the Format Specifiers tell printf ( ) where to put a value in a string and what format to use in printing that value. In this example the %d tells printf ( ) to print the value 5 as a decimal integer.%f could be used to print the 5 as a floating point number.

Printing Strings

Using Format specifiers we can print string constants as well as numbers. Here is an example that shows both a string and a number being printed together:

void main ( )

{

printf("%s is %d million miles\nfrom the sun.", "Venus", 67);

}

The output of the program will be:

Venus is 67 million miles

from the sun.

The printf ( ) has replaced the %s symbol with the string "Venus" and the %d symbol with the number 67.

Printing Characters

Printf ( ) can be used to print a single character.

void main ( )

{

printf ("The letter %c is pronounced %s.", 'j', "jay");

}

The output of the program will be:

The letter j is pronounced jay.

In this program 'j' is a character and "jay" is a string. Note that 'j' is surrounded by apostrophes while "jay" is surrounded by double quotes.