url-encode.c

	int c;
	char *hex = "0123456789abcdef";

	while( (c = getchar()) != EOF ){
		if( ('a' <= c && c <= 'z')
		|| ('A' <= c && c <= 'Z')
		|| ('0' <= c && c <= '9') ){
			putchar(c);
		} else {
			putchar('%');
			putchar(hex[c >> 4]);
			putchar(hex[c & 15]);
		}
	}