If I recall correctly, in DOS Graphics mode 13 the video buffer resided at 0xA000.
So setting a pointer to this memory location, you could write to the video buffer.
Example:
unsigned char* pVideoBuffer = 0xA000;
int x;
int y;
x = 10;
y = 10;
pVideoBuffer[ (y*320)+x ] = 0;
This would put a black pixel to 10/10 of a DOS mode 13h 320*200 Monitor in pure standard C.
( You might not have a DOS Operating System installed to try this, and it will not work on windows. Also, you have to put your DOS into 13h mode which I forgot how to do, but googling should yield some results. )
