try yourself |run program

#include <stdio.h>
#include <conio.h>

void f1(){
 int a = 100;
 int b = 200;
 printf("\n value of a = %d",a);
}

void f2(){
 printf("\n value of b = %d",b);
}

void main(){
 clrscr();
 f1();
 f2();
 getch();
}

Program Output

'b' is assigned a value that is never used
Undefined Symbol 'b'