C Programming Tutorials

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.

NEXT >> Declaration and Definition

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