You can use binary AND and OR to toggle the fourth bit.
To set the fourth bit on x, you would use x |= 1<<3;, 1<<3 being a left shift of 0b0001 by three bits producing 0b1000.
To clear the fourth bit on x, you would use x &= ~(1<<3);, a binary AND between 0b00110010 (x) and (effectively) 0b11110111, masking out every bit in x that is not in position four, thus clearing it.
