Constants in C

A constant is a value or variable that can't be changed in the program, for example: 10, 20, 'a', 3.4, "c programming" etc.

There are different types of constants in C programming.

List of Constants in C

ConstantExample
Decimal Constant10, 20, 450 etc.
Real or Floating-point Constant10.3, 20.2, 450.6 etc.
Octal Constant021, 033, 046 etc.
Hexadecimal Constant0x2a, 0x7b, 0xaa etc.
Character Constant'a', 'b', 'x' etc.
String Constant"c", "c program", "c in javatpoint" etc.

2 ways to define constant in C

There are two ways to define constant in C programming.

  1. const keyword
  2. #define preprocessor

1) C const keyword

The const keyword is used to define constant in C programming.

snippet
const float PI=3.14;

Now, the value of PI variable can't be changed.

snippet
#include  
int main(){  
	const float PI=3.14;  
	printf("The value of PI is: %f",PI);  
	return 0;
}

Output:

Output
The value of PI is: 3.140000

If you try to change the the value of PI, it will render compile time error.

snippet
#include  
int main(){  
const float PI=3.14;   
PI=4.5;  
printf("The value of PI is: %f",PI);  
	return 0;
}

Output:

Output
Compile Time Error: Cannot modify a const object

2) C #define preprocessor

The #define preprocessor is also used to define constant. We will learn about #define preprocessor directive later.

Visit here for: #define preprocessor directive.

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