Function in C Program | What is The Need Of Function | How to Write Function

C Functions

In c, we can divide a large program into the basic building blocks known as function. The function contains the set of programming statements enclosed by {}. A function can be called multiple times to provide reusability and modularity to the C program. In other words, we can say that the collection of functions creates a program. The function is also known as procedureor subroutinein other programming languages.
There are the following advantages of C functions.

By using functions, we can avoid rewriting same logic/code again and again in a program.

We can call C functions any number of times in a program and from any place in a program.

We can track a large C program easily when it is divided into multiple functions.

Reusability is the main achievement of C functions.

However, Function calling is always a overhead in a C program.

Function declaration A function must be declared globally in a c program to tell the compiler about the function name, function parameters, and return type.

Function call Function can be called from anywhere in the program. The parameter list must not differ in function calling and function declaration. We must pass the same number of functions as it is declared in the function declaration.

Function definition It contains the actual statements which are to be executed. It is the most important aspect to which the control comes when the function is called. Here, we must notice that only one value can be returned from the function

Library Functions: are the functions which are declared in the C header files such as scanf(), printf(), gets(), puts(), ceil(), floor() etc.

User-defined functions: are the functions which are created by the C programmer, so that he/she can use it many times. It reduces the complexity of a big program and optimizes the code.

function may or may not accept any argument. It may or may not return any value. Based on these facts, There are four different aspects of function calls.

function without arguments and without return value

function without arguments and with return value

function with arguments and without return value

function with arguments and with return value

Library functions are the inbuilt function in C that are grouped and placed at a common place called the library. Such functions are used to perform some specific operations. For example, printf is a library function used to print on the console. The library functions are created by the designers of compilers. All C standard library functions are defined inside the different header files saved with the extension .h. We need to include these header files in our program to make use of the library functions defined in such header files. For example, To use the library functions such as printf/scanf we need to include stdio.h in our program which is a header file that contains all the library functions regarding standard input/output.

The list of mostly used header files is given in the following table.

What is a Function in C?

Function in C programming is a reusable block of code that makes a program easier to understand, test and can be easily modified without changing the calling program. Functions divide the code and modularize the program for better and effective results. In short, a larger program is divided into various subprograms which are called as functions

When you divide a large program into various functions, it becomes easy to manage each function individually. Whenever an error occurs in the program, you can easily investigate faulty functions and correct only those errors. You can easily call and use functions whenever they are required which automatically leads in saving time and space.

Library Vs. User-defined Functions

Every ‘C’ program has at least one function which is the main function, but a program can have any number of functions. The main () function in C is a starting point of a program.

In ‘C’ programming, functions are divided into two types:

Library functions

User-defined functions

The difference between the library and user-defined functions in C is that we do not need to write a code for a library function. It is already present inside the header file which we always include at the beginning of a program. You just have to type the name of a function and use it along with the proper syntax. Printf, scanf are the examples of a library function.

Whereas, a user-defined function is a type of function in which we have to write a body of a function and call the function whenever we require the function to perform some operation in our program.

A user-defined function in C is always written by the user, but later it can be a part of ‘C’ library. It is a major advantage of ‘C’ programming.

C programming functions are divided into three activities such as,

Function declaration

Function definition