Question

I am getting ERROR when I am running this program at the line

static int b = a; //error : initializer element is not constant

Can not understand why?

 #include <stdio.h>
   // #include <setjmp.h>
    int main()
    {
    int a = 5;
    static int b = a;

    return 0;
    }

Answer 1

Apart from the other reasons stated in other answers here, please see the below statement in the Standard.

The C Standard says this in Point-4 (Section 6.7.8 Initialization):

All the expressions in an initializer for an object that has static storage duration
shall be constant expressions or string literals.

Additionally, as to what is a constant expression, it says in Section 6.6 Constant Expressions as below:

A constant expression can be evaluated during translation rather than runtime, and
accordingly may be used in any place that a constant may be.