Function in C Program

Function in C Programming Language

In this post,  We will learn about the function in c programming language. In C program a function is a block of code that does a specific task.

Type of Function in C language

There are two type of function in c programming language

1. Standard library functions
2. User-defined functions

Standard library functions

The standard library functions are built-in functions in C programming to handle tasks such as mathematical computations, I/O processing, string handling etc. these functions are defined in the header file, stdio.h is a header file, and scanf and printf function define in it.

User-defined functions

A user defines function is the functions that we define. C allows a programmer to define their own function these function called user define a function. Here we learn two basic concepts about function in c programming language.

1. How to define a function in C
2. How to call a function in C

How to define a function in C

A function contains three important parameters

1. Name of function: This is the name of a function that we want to define. Name of function can be any name except C keywords. But we should always give a proper name that reflects what function is doing. 
2. Return type of function: This is the output type of function. likes what a function well returns. for example, if the function returns an integer return type will be int. If the function does not return anything its return type will be int.
3. Argument of function: This is the input to a function. like input, the function expects from other functions.

A function structure that does not return anything and does not take any input/argument.

 void functionName()  
 {  
   ... .. ...  
   ... .. ...  
 }  

A function structure that returns an integer and does not take any input/argument.

 int functionName()  
 {  
   ... .. ...  
   ... .. ...  
   return anInteger
 }  

A function structure that returns an integer and takes an integer input/argument.

 int functionName(int args1)  
 {  
   ... .. ...  
   ... .. ...  
   return anInteger
 }  

How to Call a function in C

In C program we can call a function by its name and argument/input. We can call a function from any function.

Example call function whose name is functionName and not taking any input/argument from main.

 int main()  
 {  
   ... .. ...  
   ... .. ...  
   functionName();  
   ... .. ...  
   ... .. ...  
 }  

Example: write a program to calculate perimeter and area of a rectangle. you can take ask the user for length and width of the rectangle

 #include<stdio.h>  
 float area_rectangle(float length, float width) {  
      float area = length * width;  
      return area;  
 }  
 float perimeter_rectangle(float length, float width) {  
      float perimeter = 2 * (length + width);  
      return perimeter;  
 }  
 int main() {  
      float length;  
      float width;  
      scanf("Enter length of rectangle: %f", &length);  
      scanf("Enter width of rectangle: %f", &width);  
      float area = area_rectangle(length, width);  
      float perimeter = perimeter_rectangle(length, width);  
      printf("Area of rectangle: %f\n", area);  
      printf("Perimeter of rectangle: %f\n", perimeter);  
 }  

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.