Intermediate Programming

with C

 

Table of Contents

Introduction

Basics

Variables

Input and Output

Boolean Expressions and Branching

Loops

Functions

Files

Arrays and Pointers

 

C Programming Final Test

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 7

Functions

As we mentioned earlier, C programs are made up entirely of functions. We have already discussed the main function. Now we will discuss other functions.

As in most other programming languages, each function must have a heading. The format for a function heading is:

<return type> function name( arguments ){body}

All functions (except the main function) must also have a FUNCTION PROTOTYPE. A function prototype is simply a copy of the function's heading followed by a semicolon. It tells the compiler what each function will look like so that the compiler can look for it. See the following example. 

#include <stdio.h>


/* function prototypes */
int test_function( int x, int y);



int test_function( int x, int y) {
  int z;    /* define a local variable */

  z = x * y;
  
  return z;        /* return a value */
}



void main(void) {
  int i;

  i = test_function(2, 3);
  
  printf(" %d", i);

}

The "test_function" in this program included a few elements that require explanation. This was the first function in this tutorial to return a value. Notice that to the keyword "return" was used to return a value. The "return" keyword will terminate the current function and return its argument to the calling program. If "return" is used without an argument it will return a zero.