Constant is also known as variable where once defined, the value never changes during the program execution. Thus, we can declare a variable as constant that refers to fixed values. It is also called as literals. Const keyword has to be used to define a constant.
Syntax
The syntax for constant that is used in C programming language is given below −
const type VariableName; (or) const type *VariableName;
Different types of constants
The different types of constants that are used in C programming language are as follows −
Integer constants − For example: 1,0,34,4567
Floating-point constants − For example: 0.0, 156.89, 23.456
Octal & Hexadecimal constants − For example: Hexadecimal: 0x2a, 0xaa .. and Octal: 033, 024,..
Character constants − For example: ‘a’, ‘B’, ‘x’
String constants − For example: “TutorialsPoint”
The types of constants are also What ised in the diagram below −
Example 1
Following is the C program for determining the value of a number −
#include<stdio.h>
int main(){
const int number=45;
int value;
int data;
printf("enter the data:");
scanf("%d",&data);
value=number*data;
printf("The value is: %d",value);
return 0;
}Output
When the above program is executed, it produces the following result −
enter the data:20 The value of number is: 900
In the above program, if we try to change the value of a number which is declared as constant, it displays an error.
Example 2
Given below is the C program which gives an error, if we try to change the const value.
#include<stdio.h>
int main(){
const int number=45;
int data;
printf("enter the data:");
scanf("%d",&data);
number=number*data;
printf("The value of number is: %d",number);
return 0;
}Output
When the above program is executed, it produces the following result −
error