Adds text to current dislay line while person is typing and increases the cursor position

Adds text to current dislay line while person is typing and increases the cursor position

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Description : This is an TSR program that hooks itself with the Keyboard interrupt and after the interrupt is generated for the five times. Then it inserts the character at the current cursor position and increases the cursor position by one. The user feels that he has typed the character by mistake.

#include<dos.h>
void interrupt our();
void interrupt (*prev)();
void writechar(char ch,int row,int col,int attr);
int a,b,kp,run=0;
char far *scr;
void main()
{
scr=(char far*) 0xb8000000;
prev=getvect(9);
setvect(9,our);
keep(0,500);
}
void interrupt our()
{
kp++;
if(kp==5)
{
run++;
_AH=3;
_BH=0;
geninterrupt(0x10);
a=_DH;
b=_DL;
if(run==1)
writechar('M',a,b,7);
if(run==2)
writechar('S',a,b,7);
if(run==3)
{
writechar('P',a,b,7);
run=0;
}
b++;
_AH=2;
_BH=0;
_DH=a;
_DL=b;
geninterrupt(0x10);
kp=0;
}
(*prev)();
}
void writechar(char ch,int row,int col,int attr)
{
*(scr+row*160+col*2)=ch;
*(scr+row*160+col*2+1)=attr;
}