#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 )
{
	/* disable interrupts during the handling of
	   the interrupt */
	disable();
	/* increase the global counter */
	count++;
	/* reenable interrupts at the end of the
	   handler */
	enable();
	/* 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;
}