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Functions

A function is a group of statements that together perform a task. Every C program has at
least one function, which is main(), and all the most trivial programs can define additional
functions.
You 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 is such that each function
performs a specific task.
A function declaration tells the compiler about a function's name, return type, and
parameters. A function definition provides the actual body of the function.
The C standard library provides numerous built-in functions that your program can call.
For example, strcat() to concatenate two strings, memcpy() to copy one memory location to
another location, and many more functions.
A function can also be referred as a method or a sub-routine or a procedure, etc.

Defining a Function
The general form of a function definition in C programming language is as follows:
A function definition in C programming consists of a function header and a
function body. Here are all the parts of a function:

return_type function_name( parameter list )
{

body of the 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.

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