Using Functions

A function is a module or block of program code which deals with a particular task. Making functions is a way of isolating one block of code from other independent blocks of code.

Functions serve two purposes.

• They allow a programmer to say: `this piece of code does a specific job which stands by itself and should not be mixed up with anything else',

• Second they make a block of code reusable since a function can be reused in many different contexts without repeating parts of the program text.

A function can take a number of parameters, do required processing and then return a value. There may be a function which does not return any value.

You already have seen couple of built-in functions like printf(); Similar way you can define your own functions in C language.

Consider the following chunk of code

int total = 10; printf("Hello World"); total = total + l;

To turn it into a function you simply wrap the code in a pair of curly brackets to convert it into a single compound statement and write the name that you want to give it in front of the brackets:

Demo() { int total = 10; printf("Hello World"); total = total + l; }

curved brackets after the function's name are required. You can pass one or more parameters to a function as follows:

Demo( int par1, int par2) { int total = 10; printf("Hello World"); total = total + l; }

By default function does not return anything. But you can make a function to return any value as follows:

int Demo( int par1, int par2) { int total = 10; printf("Hello World"); total = total + l; return total; }

A return keyword is used to return a value and datatype of the returned value is specified before the name of function. In this case function returns total which is int type. If a function does not return a value then void keyword can be used as return value.

Once you have defined your function you can use it within a program:

main() { Demo(); }

Functions and Variables:
Each function behaves the same way as C language standard function main(). So a function will have its own local variables defined. In the above example total variable is local to the function Demo.

A global variable can be accessed in any function in similar way it is accessed in main() function.