DEFINATION—A function is a group of statements that together perform a task. Every C program has at least one function, which is main(),

We can divide up your code into separate functions. How you divide up your code among different functions is up to you, but logically the division usually is so each function performs a specific task.

A function declaration tells the compiler about a function’s name, return type, and parameters. A function definitionprovides the actual

Defining a Function:

The general form of a function definition in C programming language is as follows:

return_type function_name( parameter list )
{
   body of the function
}

body of the function.

A function definition in C programming language consists of a function header and a function body. Here are all the parts of a function:

• Return Type: A function may return a value. The return_type is the data type of the value the function returns. Some functions perform the desired operations without returning a value. In this case, the return_type is the keyword void.
• Function Name: This is the actual name of the function. The function name and the parameter list together constitute the function signature.
• Parameters: A parameter is like a placeholder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters.
• Function Body:The function body contains a collection of statements that define what the function does.
  

  Function Declarations:

  A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately.

  A function declaration has the following parts:

  return_type function_name( parameter list );

  Calling a Function:

  While creating a C function, you give a definition of what the function has to do. To use a function, you will have to call that function to perform the defined task.

  When a program calls a function, program control is transferred to the called function. A called function performs defined task and when its return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program.

  To call a function, you simply need to pass the required parameters along with function name, and if function returns a value, then you can store returned value

Function Arguments:

If a function is to use arguments, it must declare variables that accept the values of the arguments. These variables are called the formal parameters of the function.

The formal parameters behave like other local variables inside the function and are created upon entry into the function and destroyed upon exit.

While calling a function, there are three ways that arguments can be passed to a function:

1.call by value

2.call by reference

3.call by pointers.