constant

constant is an modifier of data type in c

const data_type var_name;

const int data;

we can only assign the value to the constent variable at the time of declaration.
after declaration, we can't assign/modify the value to the constant variable
the exeucution time of constant variable is faster as compare to another variable.

Rules:

constant modifier can not be used with void, enum and function.

Advanced reader:

We can modify the value of constant variable using pointer.

C Programming