Mirror your DOS screen

Mirror your DOS screen

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Description : This is a TSR program which hooks itself with the timer interrupt and changes the current DOS screen with its mirror image i.e. character on the first line will be displayed on the last and on last will be displayed on first.

#include"dos.h"
void interrupt (*prevtimer)();
void interrupt mytimer();
void writechar(char ch,int row,int col,int attr);
int ticks=0;
int running=0;
unsigned long far *time=(unsigned long far*) 0x46c;
char far* scr;
char far* mode;
void main()
{
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()
{
int i,j,k;
char t[80];
ticks++;
if(ticks==18)
{
ticks=0;
if(running==0)
{
running=1;
}
for(i=0;i<25;i++)
{
for(k=0;k<=79;k++)
{
t[k]=*(scr+i*160+k*2);
}
k=0;
for(j=79;j>=0;j--)
{
writechar(t[k],i,j,7);
k++;
}
}
}
running=0;
(*prevtimer)();
}
void writechar(char ch,int row,int col,int attr)
{
*(scr+row*160+col*2)=ch;
*(scr+row*160+col*2+1)=attr;
}