FUNCTIONS :

User‐Defined Functions :

A function is a block of code/group of statements/self contained block of statements/ basic building blocks in a program that performs a particular task. It is also known as procedure or subroutine or module, in other programming languages. 

To perform any task, we can create function. A function can be called many times. It provides modularity and code reusability. 

Advantage of functions

 1) Code Reusability By creating functions in C, you can call it many times. So we don't need to write the same code again and again. 

2) Code optimization It makes the code optimized we don't need to write much code. 

3) Easily to debug the program. 

Types of Functions

 There are two types of functions in C programming: 

1. Library Functions: are the functions which are declared in the C header files such as scanf(), printf(), gets(), puts(), ceil(), floor() etc. You just need to include appropriate header files to use these functions. These are already declared and defined in C libraries. oints to be Remembered System defined functions are declared in header files System defined functions are implemented in .dll files. (DLL stands for Dynamic Link Library). To use system defined functions the respective header file must be included. 

2. User-defined functions: are the functions which are created by the C programmer, so that he/she can use it many times. It reduces complexity of a big program and optimizes the code. Depending upon the complexity and requirement of the program, you can create as many user-defined functions as you want .

ELEMENTS OF USER-DEFINED FUNCTINS : 

In order to write an efficient user defined function, the programmer must familiar with the following three elements. 

1 : Function Declaration. (Function Prototype).

 2 : Function Call.

 3 : Function Definition 

Function Declaration. (Function Prototype).

 A function declaration is the process of tells the compiler about a function name.

 Syntax return_type function_name(parameter/argument); 

return_type function-name();

 Ex : int add(int a,int b);

 int add(); 

Calling a function/function call :

When we call any function control goes to function body and execute entire code. Syntax : function-name(); function-name(parameter/argument); return value/ variable = function-name(parameter/argument); 

Defining a function:

Defining of function is nothing but give body of function that means write logic inside function body. Syntax return_ type function-name(parameter list)