We use the const qualifier to declare a variable as constant. That means that we cannot change the value once the variable has been initialized. Using const has a very big benefit. For example, if you have a constant value like the value of PI, you wouldn't like any part of the program to modify that value. So you should declare that as a const.
Objects declared with const-qualified types may be placed in read-only memory by the compiler, and if the address of a const object is never taken in a program, it may not be stored at all. For example,
#include<iostream> using namespace std; int main() { const int x = 10; x = 12; return 0; }
This program would produce an error as we have tried to reassign a const value.