#include <stdio.h>

#define SCREEN_HEIGHT 22
#define SCREEN_WIDTH  78

// Simulated frame buffer
char Screen[SCREEN_HEIGHT][SCREEN_WIDTH];

void SetPixel(int x, int y, char color)
{
  if ((x < 0) || (x >= SCREEN_WIDTH) ||
      (y < 0) || (y >= SCREEN_HEIGHT))
    return;

  Screen[y][x] = color;
}

void Visualize(void)
{
  int x, y;

  for (y = 0; y < SCREEN_HEIGHT; y++)
  {
    for (x = 0; x < SCREEN_WIDTH; x++)
      printf("%c", Screen[y][x]);

    printf("\n");
  }
}

typedef struct
{
  int x, y;
} Point2D;

int main(void)
{
  // triangle vertices
  Point2D vx0 = { SCREEN_WIDTH / 2, SCREEN_HEIGHT / 7 };
  Point2D vx1 = { SCREEN_WIDTH * 6 / 7, SCREEN_HEIGHT * 2 / 3 };
  Point2D vx2 = { SCREEN_WIDTH / 7, SCREEN_HEIGHT * 6 / 7 };
  // vectors lying on triangle sides
  Point2D v0, v1, v2;
  // current point coordinates
  int x, y;

  // calculate side vectors

  v0.x = vx1.x - vx0.x;
  v0.y = vx1.y - vx0.y;

  v1.x = vx2.x - vx1.x;
  v1.y = vx2.y - vx1.y;

  v2.x = vx0.x - vx2.x;
  v2.y = vx0.y - vx2.y;

  // process all points

  for (y = 0; y < SCREEN_HEIGHT; y++)
    for (x = 0; x < SCREEN_WIDTH; x++)
    {
      int z1 = (x - vx0.x) * v0.y - (y - vx0.y) * v0.x;
      int z2 = (x - vx1.x) * v1.y - (y - vx1.y) * v1.x;
      int z3 = (x - vx2.x) * v2.y - (y - vx2.y) * v2.x;

      if ((z1 * z2 > 0) && (z1 * z3 > 0))
        SetPixel(x, y, '+'); // point is to the right (left) of all vectors
      else
        SetPixel(x, y, '-');
    }

  // draw triangle vertices

  SetPixel(vx0.x, vx0.y, '0');
  SetPixel(vx1.x, vx1.y, '1');
  SetPixel(vx2.x, vx2.y, '2');

  // visualize the result

  Visualize();

  return 0;
}