#include <conio.h>

unsigned char *video_memory = (unsigned char *) 0xA0000000L;

void init_mode13h()
{
 asm {
  mov ax, 0x13
  int 0x10
 }
}

void put_pixel(int x, int y, unsigned char color)
{
 video_memory[y * 320 + x] = color;
}

void init_textmode()
{
 asm {
  mov ax, 0x3
  int 0x10
 }
}

void main()
{
 init_mode13h();
 put_pixel(4, 3, 4); // 4 = RED
 getch();
 init_textmode();
}