Q1:

What is the output of the program?

#include<stdio.h>
int main()
{
    extern int a;
    printf('%d\n', a);
    return 0;
}
int a=20;

extern int a; indicates that the variable a is defined elsewhere, usually in a separate source code module. printf('%d\n', a); it prints the value of local variable int a = 20. Because, whenever there is a conflict between local variable and global variable, local variable gets the highest priority. So it prints 20.