main()
{
extern int i;
i=20;
printf("%d",i);
}


Answer:
Linker Error : Undefined symbol '_i'


Explanation:
extern storage class in the following declaration,
extern int i;
specifies to the compiler that the memory for i is allocated in some other program and that address will be given to the current program at the time of linking. But linker finds that no other variable of name i is available in any other program with memory space allocated for it. Hence a linker error has occurred .