C Tutor... C Tutorial....: A TSR CLOCK

#include "dos.h"

void interrupt ( *prevtimer )( ) ;
void interrupt mytimer( ) ;

int running = 0 ;
unsigned long far *time = ( unsigned long far * ) 0x46C ;
char far *scr ;
char far *mode ;

main( )
{

/* peek into location 0:410h and determine video mode */
if ( ( *mode & 0x30 ) == 0x30 )
scr = ( char far * ) 0xB0000000 ;
else
scr = ( char far * ) 0xB8000000 ;

prevtimer = getvect ( 8 ) ;
setvect ( 8, mytimer ) ;
keep ( 0, 1000 ) ;

}

void interrupt mytimer( )
{
unsigned char hours, sec, min ;

if ( running == 0 )
{

running = 1;
hours = ( *time / 65520 ) ;
min = ( *time - hours * 65520 ) / 1092 ;
sec = ( *time - hours * 65520 - min * 1092 ) * 10 / 182 ;

if ( sec >= 60 )
{

sec -= 60 ;
min++ ;

if ( min == 60 )
{

min = 0 ;
hours++ ;

if ( hours == 24 )
hours = 0 ;

}

}

/* display digital clock */
writechar ( 48 + hours / 10, 0, 72, 112 ) ;
writechar ( 48 + hours % 10, 0, 73, 112 ) ;
writechar ( ':', 0, 74, 112 ) ;
writechar ( 48 + min / 10, 0, 75, 112 ) ;
writechar ( 48 + min % 10, 0, 76, 112 ) ;
writechar ( ':', 0, 77, 112 ) ;
writechar ( 48 + sec / 10, 0, 78, 112 ) ;
writechar ( 48 + sec % 10, 0, 79, 112 ) ;

running = 0 ;

}

( *prevtimer )( ) ;

}

writechar ( char ch, int row, int col, int attr )
{

*( scr + row * 160 + col * 2 ) = ch ;
*( scr + row * 160 + col * 2 + 1 ) = attr ;

}

Related Links :

History Of C..

In the beginning was Charles Babbage and his Analytical Engine, a machine
he built in 1822 that could be programmed to carry out different computations.
Move forward more than 100 years, where the U.S. government in
1942 used concepts from Babbage’s engine to create the ENIAC, the first
modern computer.
Meanwhile, over at the AT&T Bell Labs, in 1972 Dennis Ritchie was working
with two languages: B (for Bell) and BCPL (Basic Combined Programming
Language). Inspired by Pascal, Mr. Ritchie developed the C programming
language.