Program for Resolving Variable Reference with Explanation

Program

int i =0;            //Global variable  /A
main()
{
    int i ;                 // local variable for main  / B
    void f1(void) ;         //C
    i =0;                   // D
    printf("value of i in main %d\n",i);   // E
    f1();                                  // F
    printf("value of i after call%d\n",i); // G
}
void f1(void)                       // H
{
    int i=0;          //local variable for f1      // I
    i = 50;                                // J
}

Explanation

1. Here i is declared globally and locally in function main and in function f1, respectively, as given in statements A, B and I.
2. Statement D refers to i, which can be resolved by using both local definition and global definition. Local definition is given more preference. So statement D refers to the definition at statement B and all the statements in main refer to the definition at statement B, that is, the local definition.
3. When a function is called, statement i = 50 refers to the local definition in that function (definition at statement I).
4. Using statement G, the value of i is 0 because both main and function f1 refer to their local copies of i. So the changed value of f1 is not reflected in main.
5. Even if you comment local definition of function f1 at statement I the value printed remains the same. This is because main refers to its local copy while f1 refers to the global variable i — the two are different.