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Table of contents
1.
Introduction
2.
Types of Functions
2.1.
Library Functions
2.2.
User-defined Functions 
3.
Advantages of Using Functions in C Programming
4.
Defining a Function
4.1.
Syntax
4.2.
Function declaration consists of 4 parts.
4.2.1.
Function Name:
4.2.2.
Function Body 
4.2.3.
Parameters
4.2.4.
Return Type 
5.
Calling a Function
5.1.
Example
6.
Return Value
6.1.
Example without return value:
6.2.
Example with return value:
7.
Function Arguments
7.1.
Call by value
7.2.
Call by reference
8.
Library Functions In C
9.
Frequently Asked Questions
10.
Key Takeaways
Last Updated: Mar 27, 2024

Introduction to Functions

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Introduction

A function is a set of all the statements put together to perform a required task. It could be statements making some repeated work or doing a little specialty task like printing etc. One of the uses of a function is to simplify the code by breaking it into smaller functions, but another thing behind using functions is that it saves us from writing the same code again. We have to write that function once and then call it whenever required without writing the same statement set again and again.

Also see, Literals in C and C Static Function

Types of Functions

Library Functions

Library functions are the functions that are already defined in the C library, for example, printf(), scanf(),strcat(), and so on. You want to include appropriate header files to use those functions. Those are already declared and defined in C libraries.

User-defined Functions 

User-defined functions, then again, are the capabilities that the user defines at the time of writing the program. Those functions are made for code reusability and for saving time and space.

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Advantages of Using Functions in C Programming

  • Using functions, we will avoid rewriting the same common sense/code again and again in a program.
  • We will name C functions any number of times in a program and from any area.
  • We will effortlessly track a big C program when divided into multiple functions.
  • Reusability is the primary achievement of C functions.
  • However, the function call is always overhead in a C program.

 

You can also read about the jump statement and  Short int in C Programming

Defining a Function

Syntax

return type functionName(type1 parameter1, type2 parameter2,...)
{
    // function body goes here
}

Function declaration consists of 4 parts.

Function Name:

The function name is an identifier, and it specifies the function's name. The function name is another valid C identifier and therefore should comply with the same naming policies like different variables in the c language.

Function Body 

It includes a set of all the statements. Those define what the function will do within the code.

Parameters

The parameter listing declares the sort and number of arguments that the function expects while it is called. Additionally, the parameters within the parameter list receive the argument values when the function is called. They're often referred to as formal parameters.

Return Type 

When a function is declared to perform any calculation or any operation and is expected to offer with some result at the cease, in such cases, a return statement is added on the end of the function body. Return type specifies the value(int, float, char, double) that function is expected to return to the program, called the function.

Also See, Sum of Digits in C, Tribonacci Series

Calling a Function

While creating a C function, you define what the function has to do. To use a function, you'll have to call that specific function to perform the desired task. When a program calls that specific function, the program management is referred to as function. A called function performs a defined task, and when its return statement is performed or its function-ending closing brace is reached, it returns the program control to the main program.

To call a function, you need to pass the required parameters together with the function name, and if the function returns a value, you could store the returned value.

Example

#include <stdio.h>
int max(int num1, int num2);
int main () 
{
   int a = 100;
   int b = 200;
   int ret;
   ret = max(a, b);
   printf( "Max value is : %d\n", ret ); 
   return 0;
}
int max(int num1, int num2) 
{
   int result;
   if (num1 > num2)
      result = num1;
   else
      result = num2;
   return result; 
}

Output

Max value is: 200

Return Value

A function of C can also or might not return a value from the function. If you do not have to return any value from the function, use void for the return type;

Example without return value:

void hello()
{  
	printf("hello c");  
}  

When you want to return any value from the function, you need to apply any data type together with int, long, char, and others, and the return type depends on the value to be returned from the function.

Example with return value:

int get()
{  
	return 10;  
} 

Function Arguments

If a function requires arguments, it must declare variables that take delivery of the values of the arguments. Those variables are called the formal parameters of the function.

Formal parameters behave like other local variables inside the function and are created upon access into the function and destroyed upon going out.

while calling a function, there are two ways wherein arguments may be surpassed to a function −

Call by value

This approach copies the real value of an issue into the function's formal parameter. In this situation, changes made to the parameter in the function do not affect the argument.

Call by reference

This method copies the address of controversy into the formal parameter. The address is used to enter the real argument used inside the call in the function. Because of this, changes made to the parameter affect the argument.


Check out this problem - Redundant Braces

Library Functions In C

Library functions are the built-in functions in C grouped and placed at a not unusual location known as the library. Such functions are used to perform particular operations. For example, the printf library function is used to print at the console. The library functions are created through the designers of the compilers. We can define all C standard library functions inside the different header files stored with '.h.' We just need to include these header files in our program to use the library functions defined in such header files. For example, to apply library functions such as printf/scanf, we want to include stdio.h in our program, a header file containing all of the library functions regarding standard input/output.

Mainly used header files are given in the following table:

Header file                                     Description
stdio.h This is a popular input/output header file. It consists of all the library functions concerning popular input/output.
conio.h That is a console input/output header file.
string.h It consists of all string-related library functions like gets(), puts(), etc.
stdlib.h This header file contains all the overall library functions like malloc(), malloc(), exit(), and so on.
math.h This header file consists of all the math operations-related functions like sqrt(), pow(), and so on.
time.h This header file contains all of the time-related functions.
ctype.h That header file contains all character handling functions.
stdarg.h   Variable argument functions are defined on this header file.
signal.h All of the signal handling functions are described in this header
setjmp.h This file contains all the jump functions.
locale.h This file consists of locale functions.
errno.h This file includes errors dealing with functions.
assert.h This report consists of diagnostics functions.

 

You can also read about dynamic array in C.

Frequently Asked Questions

1. What are the different aspects of function calls?

Ans: The functions to be had in a code may additionally take delivery of an issue or may not take delivery of it at all. Hence, it can return any of the values or won't do so. On the idea of those facts, the function calls have the following aspects:

  • Function with no arguments and no return value.
  • Function with no arguments but has a return value.
  • A function that has views, however, has no return value.
  • A function that has ideas and also has a return value.


2. Why do we need to declare a function in a program?

Ans: The function definition tells a compiler about the name of the function and easy methods to call this function. Then we will define the real body of this function separately.

There are the following parts that exist in a function declaration:

return_type name_of_function( parameter list );


3. what is the importance of calling a function?

Ans: While we create a function in C programming, we offer that function to define what it must do. However, we want to call it its defined task to apply this function.

When a function receives called by way of a program, the called function gets the program control transferred to it. The called function will present a defined task. Once we execute the go-back statement or reach the function's ending final brace, it is sure to return the control to the main program.

We surely need to skip the parameters required for it, together with the call of the function for calling a function. Here, if the function returns a fee, we can easily save the returned value.

Key Takeaways

We learned about the type of all functions and their use. We learned functions that reduce code redundancy. Functions make code modular. Don't forget a large report having multiple lines of code. It will become simple to examine and use the code if it is divided into functions. For more exercise, you can visit interview Experiences of top tech companies for practice.

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Function Prototype
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