Functions are an essential part of programming in C. They allow you to break down your code into smaller, reusable blocks of code, making it easier to understand, debug, and maintain. In this guide, we will take a detailed look at functions in C programming, covering their syntax, types, parameters, return values, and best practices.

Functions in C Programming Language

The fundamental building blocks of a C programme are functions. A function is a collection of instructions denoted by a set of curly brackets () that accept inputs, perform calculations, and output the results. C programming supports modularity and reuse by enabling many calls to the same function. This implies that you can call a function several times by just giving different arguments, rather than having to write the same code repeatedly for different inputs. Let us understand more about the functions in C programming.

Requirement of Functions in C Programming Language

Because of the many benefits they offer to the developer, functions are essential to C programming and even to other programming languages. The use of functions has several major advantages, including:

  • Lowers redundancy and permits reusability
  • Modularizes a code
  • Provides an abstraction feature
  • The software becomes simple to use and comprehend
  • Divides a complex programme into smaller, easier bits

Syntax of a Function


A function body and a function header make up a function in C. The function header declares the function’s name, return type, and any parameters it takes. The function body contains the actual code. When the function is called, the code gets executed.

Here’s the general syntax of a function in C:

return_type function_name (argument list)
    Group of statements – Code to be executed

In the syntax above,

  • return_type: Return type usage includes any data type, including int, double, char, void, and short. 
  • function_name: It can be anything, but it is encouraged to give each function a meaningful name so that its purpose can be inferred just from looking at it.
  • argument list: The names of the variables and their data types are listed in the argument list. These arguments serve as inputs for the function. For instance, a function that adds two integer variables will have two integer arguments.
  • Code to be executed: It represents a collection of C statements that will run each time the function is called.

Types of Functions in C Programming Language

There are two categories of functions in C Programming:

Library Functions

Library functions, often known as predefined functions, are predefined in the C libraries. This means that to call them, we do not need to write a definition or the function’s body. Since they are already defined, we can just call them instead of defining them. To call a library function, however, the library must be included at the beginning of the code. Then, we may call them using the function’s proper syntax. Library functions include printf(), scanf(), ceil(), and floor(), for instance.

User-Defined Functions

These are the functions that are declared, defined, and called by a developer or user in a programme. The flexibility to define and use any function boosts the reach, functionality, and reuse of C programming. The key benefit of C programming language is the ability to add a user-defined to any library and use it in other programmes.

In C, How do You Call a Function?

There are four distinct characteristics of C function calls, depending on whether the function accepts arguments or not and whether it returns a value or not. These include:

1. Functions in C Programming Without Arguments and Return Value

In C programming, a function cannot take an argument and return a value. Here is an illustration of one such function.


void main (){

    printf("Welcome to ");



void printName(){  

    printf("Henry Harvin");



Welcome to Henry Harvin

2. Functions In C Programming With Arguments but Without Return Value

Although C functions don’t always return a value, they may receive arguments. An illustration of such a function is shown below.


void main(){

    int x,y;    

    printf("Enter the two numbers to add:");

    scanf("%d %d",&x,&y);



// Accepting arguments with void return type

void add(int x, int y){

    printf("The sum of the numbers is %d",x+y);



Enter the two numbers to add: 7        6
The sum of the numbers is 13

3. Functions in C Programming That Take No Arguments But Return A Value

Without taking any input, a function can return a value. Here is an illustration of how to compute and return a rectangle’s area without using any arguments.


void main(){

    int area = rect_Area();

    printf("The area of the Rectangle is: %d\n",area);


int rect_Area(){

    int len, wid;    

    printf("Enter the length of the rectangle: ");


    printf("Enter the width of the rectangle: ");


    return len * wid;



Enter the length of the rectangle: 5
Enter the width of the rectangle: 6
The area of the Rectangle is: 30

4. Functions in the C programming language that Take Arguments and Provide a Return Value

The majority of C functions take parameters and return a value. The function that receives parameters and returns a value in C programming is shown in the following programme.


void main(){

    int x,y,res;    

    printf("Enter the two numbers to add:");

    scanf("%d %d",&x,&y);    

    res = add(x,y);

    printf("The sum of the numbers is %d",res);


int add(int x, int y){

    return x+y;



Enter the two numbers to add: 8    9
The sum of the numbers is 17

Important Information to Remember Regarding Functions in C Programming

  • In C, each programme has a function. You must utilise the main function even if you don’t use a library or user-defined function. The program’s entry point, where the compiler will begin running the code, is the main function.
  • A function still has a return type even if it doesn’t produce a value. If a return value is given, the data type of the value serves as the return type. However, the function’s return type is void if there is no return value.
  • Array and function types cannot be returned by C functions. The usage of pointers, however, makes it simple to get around this restriction.
  • The terms void func() and void func(void) are equivalent in C++, but not in C programming. A function can be called in C with any number of parameters even if it is declared without a parameter list. Therefore, if you want to call a function without passing any parameters, it is best to declare it as void func(void) rather than void func().
  • If you call a function before it is declared, the C compiler will automatically assume that the return type is an int. It will display an error if the return value’s data type is anything other than an int.


You have learnt everything there is to know about functions in C programming in this article. A C program’s fundamental building blocks are functions. They offer the benefits of simplicity, modularity, and reuse. Therefore, to optimise your programme, you must learn how to build and use functions. By taking the C++ course on Henry Harvin, you can learn more about such C essentials. The website provides free training in a variety of programming languages, including C. You can enrol, choose the course you wish to take, and learn the fundamentals of that programming language.

C++ Course by Henry Harvin

Functions in C Programming Language
  • Discover the top-rated C++ Foundation course in India, offering an exceptional learning environment. 
  • Gain expertise in advanced C programming, delve into essential concepts and become a master of the powerful and versatile programming language, C++. 
  • Engage in comprehensive hands-on training, tackling authentic coding problems for a truly immersive learning experience.

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