// flip an image upside-down
//
#include "ppm.h"

void flip( unsigned char *x[], int m) { // same as: unsigned char **x
  for( int i = 0, j = m-1; i < j; ++i, --j) {
    unsigned char *t = x[i]; x[i] = x[j]; x[j] = t; // swap row i,j pointers
  }
}

int main( void)
{
  ppm a = ppm_read();
  flip(a.r,a.rows);
  flip(a.g,a.rows);
  flip(a.b,a.rows);
  ppm_write( a);
  return 0;
}