Write a function

Q. How to write a function and why we need them?

Ans. First of all why we need function.

Suppose we have to write a programme for L.C.M. (least common multiple) for two integers . We wrote the programme without using function and someone now ask to write the same programme for more than two integers. But now we cannot use the same programme for it. But If we would have written that programme in a function then we could have used that function for extension.

If we have to find the l.c.m. twice in the same programme then we have to write the code twice if we are not making a function of the l.c.m.

There are more advantages.

1. We don't have to rewrite the code again and again. (Code length is reduced)

2. We can use those function in other programmes but if do not write in functions we can not re use them. (Extendability)

3. Easy to read and understand. (User and programmer friendly)

How to write functions?

Functions always have their prototype. Means what is the function's name and what function take as argument and what does function return etc.. I will explain it in the next part.

Prototype:(function declaration)

Return_type function_name ( function's arguments);

Ex.  int add(int val1, int val2);

In this prototype function's return type is int means function will return a integer. Function name is add and it takes two argument val1 and val2. It is just a prototype. Function will also have a body. In which we define what function really does?

(function definition)

Ex.

 int add(int val1, int val2){             //function body starts

      int result= val1+val2;

      return result;

}

Function's body is written between the paranthesis. Here we define a temporarily variable which is not necessary. We add the two values and return the result through return keyword.

We could have written it this way also.

int add(int val1,int val2){

       return val1+val2;

}

This is also correct. It automatically allocate a temporarily variable and calculate the result and then return the result.

Prototype is not necessary if you define function before it is used. But now in new gcc compiler (2014) there is no need to write prototype or declaration . You can directly define function anywhere in the programme. Remember it is true only for the latest gnu gcc compiler.