make checkers

gistfile1.txt

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

//
// checker 17 11 > ch17_11.pgm
//

int main(int argc, char **argv)
{
	int w=argc>1?atoi(argv[1]):15;
	int h=argc>2?atoi(argv[2]):9;
	int b=argc>3?atoi(argv[3]):64;  // must be pow2 !!
	int ww = ( w + 2 ) * b;
	int hh = ( h + 2 ) * b;
	printf("P6\n%d %d\n255\n", ww, hh);
	for ( int i = 0; i < hh; i++) {
		for ( int j = 0; j < ww; j++) {
			if ( i<=b || i>=hh-b || j<=b || j>=ww-b) {
				putc(255,stdout);
				putc(255,stdout);
				putc(255,stdout);
				continue;
			}
			unsigned char c = ((((i&b)==0)^((j&b)==0)))*255;
			putc(c,stdout);
			putc(c,stdout);
			putc(c,stdout);
		}
	}
	return 0;
}