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What is a Function in C Programming?

In particular, the Input-Output Function, Main Function, and Pre-defined Function will be highlighted in this article as different categories of functions in the C programming language. It will also draw attention to the benefits that C language programmers get from employing these functions.

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Understanding Functions in C Language

A function in C is a chunk of code that performs a specified task. They are used to break down code into smaller, more manageable chunks that may then be called from other portions of a program to accomplish their unique duty. In C language, a function can take zero or more parameters and return a value or nothing at all.

Before a function can be used, it must be declared, and this declaration includes information like the function’s name, return type, and parameter types. Later in the program, with the actual code that does the task, the function is defined. Once defined, a function can be called from any portion of the program where it is visible. Functions are a fundamental notion in C programming that is frequently used in the development of larger, more complicated programs.

Why are Functions necessary in C Programming?

Due to their potential to produce more effective, understandable, and manageable code, functions are a crucial tool in the world of C programming. Functions are used for a variety of things in C programming. Here are some of the main rationales as to why functions are required in C.

Types of Functions in C Programming

Types of Functions in C Programming

The C programming language includes a variety of functions, which are enumerated below.

Example: int main(void) {
    // code to be executed
    return 0;

Pre-Defined Functions in C Language

The C language has been equipped with a large number of built-in functions, which are easily available in the C library. These pre-programmed functions are engineered to carry out specific actions, including arithmetic computations, input/output procedures, and textual manipulations. Mentioned below are some of the pre-programmed functions in the C language.

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Input-Output Functions in C Programming

Input-Output Functions in C Programming

Users can read user input and see data displayed using input-output functions. Both engaging with users and processing data depend on these features. As previously mentioned, the C header file includes input and output functions like ‘scanf()’ for input and ‘printf()’ for output.   

Let’s examine some of the most common input functions.

For integers, use %d.
For floating-point numbers, use %f.
For characters, use %c.
For strings, use %s

For instance, the code snippet below makes use of printf to display the value of an integer variable.

int num = 23;
printf("The value of num is %dn", num);

The following text will appear on the screen as a result

The value of num is 23

As an illustration, the code snippet below makes use of scanf to read an integer value from the keyboard

int num;
printf("Enter a number: ");
scanf("%d", &num);
printf("You entered %dn", num);

This program reads the user’s entered number from the keyboard, prompts them to enter a number, and then writes it back on the screen.

Let’s now look at some of the most used output routines.

The ability to wait for user input before continuing execution makes this function helpful for interactive programs. Getchar() is used to read a single character from the user, to put it simply. This is how its syntax looks

int getchar(void);

For instance, the following line of code reads a single character from the keyboard and outputs its ASCII code.

int ch;
printf("Enter a character: ");
ch = getchar();
printf("The ASCII code of %c is %dn", ch, ch);

This program asks the user to enter a character, then reads the character from the keyboard and prints its ASCII code.

To write a single character to the screen or a file, use the putchar function. It just needs one argument, which is the character’s ASCII code. The syntax is as follows

int putchar(int c);

For example, the following code snippet uses putchar to print the characters ‘S’, ‘p’, ‘a’, ‘r, ‘d’, ‘n’ to the screen


This program prints the word “Spardn” to the screen when it runs.

Main Functions in C Programming

In C, even if you don’t use user-defined functions or a library, you must use the main function, as it is the first function that is executed when the program is run. The main function can call other functions to perform specific tasks. The exit status of a program is determined by the main function’s return of an integer value to the operating system.

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Creating User-Defined Functions in C Language

Creating User-Defined Functions in C Language

User-defined functions, as the name suggests, are custom functions created by the user or programmer, according to their own need, to perform specific tasks. To create a user-defined function in the C language, the steps given below need to be followed.

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Advantages of Functions in C Language

Functions in the C language offer numerous benefits, thus making them an indispensable tool for any programmer. The following are some key advantages of functions:


Functions are a fundamental notion in C programming. They provide a reusable tool for completing repetitive activities. Functions also help organize the code into smaller, more manageable chunks, thus providing a level of abstraction that makes complex programs easier to understand and deal with. The C programming language offers various kinds of functions, including library functions, user-defined functions, and main functions. The input/output functions are used to read user input and display output to the user. Predefined functions are already present in the C library and can be used to execute specified tasks.

If you have any doubts, drop them on our C Community!

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