#include <stdio.h>
#include <stdlib.h>

typedef struct {
  int xpos;
  int ypos;
} Point;

const int MAX_PTS=100;
const int DIM=20;
const char BLANK=' '; const char POINT='X';

int loadPoints(char * fileName,Point list[]); // returns number loaded
void plotPoints(Point list[], int count); 


int main(int argc, char * argv[]) {
  Point listing[MAX_PTS];
  int count = loadPoints(argv[1],listing);
  plotPoints( listing, count);
  return 0;
}


// loads points from file
// assumes number of points given at start of file
int loadPoints(char* fileName, Point list[]) {
  FILE* inFile;
  inFile = fopen(fileName, "r"); 
  if( inFile==NULL ) {
    printf("Couldn't find file %s\n", fileName);
    return 0;
  }

  int p, limit;
  fscanf(inFile, "%d", &limit);
  if(limit>MAX_PTS) {
    printf("Only taking first %d points\n", MAX_PTS);
    limit = MAX_PTS;
  }
  for(p=0; p<limit; p++) 
    fscanf(inFile, "%d%d", &list[p].xpos, &list[p].ypos);

  fclose(inFile);  
  return limit;
}

 
// plots points on a grid of DIM x DIM
// assumes coordinates in range 0..DIM-1
void plotPoints(Point list[], int count) {
  char screen[DIM][DIM];
  int i,j,p;
  for(i=0; i<DIM; i++)
    for(j=0; j<DIM; j++)
      screen[i][j] = BLANK;
  for(p=0; p<count; p++) 
    if(list[p].xpos>=0 && list[p].xpos<DIM && list[p].ypos>=00 && list[p].ypos<DIM )
      screen[ list[p].xpos ][ list[p].ypos ] = POINT;
   
  for(i=0; i<DIM; i++) {
    for(j=0; j<DIM; j++)
      printf("%c", screen[i][j] );
    printf("\n");
  }
}