/***NOTE: 
    This is an interrupt service routine.  You can NOT compile this 
    program with Test Stack Overflow turned on and get an executable 
    file which will operate correctly. */ 

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

#define INTR 0X1C    /* The clock tick interrupt */ 

void interrupt ( *oldhandler)(void); 

int count=0; 

void interrupt handler(void) 
{ 
/* increase the global counter */ 
   count++; 

/* call the old routine */ 
   oldhandler(); 
} 

int main(void) 
{ 
/* save the old interrupt vector */ 
   oldhandler = getvect(INTR); 

/* install the new interrupt handler */ 
   setvect(INTR, handler); 

/* loop until the counter exceeds 20 */ 
   while (count < 20) 
      printf("count is %d\n",count); 

/* reset the old interrupt handler */ 
   setvect(INTR, oldhandler); 

   return 0; 
}