Set, Clear & Toggle a Bit

Sometimes you need to change a single bit without touching the others. The trick is building a mask that targets exactly the bit you want. 🎯

Shift 1 to the position you care about and you get a mask with one bit on. Position 0 is the rightmost bit.

To turn a bit on, OR the number with the mask. OR forces that position to 1 and leaves every other bit alone. We call this setting a bit.

If the bit is already 1, setting it again changes nothing. OR with a mask is safe to repeat, which makes it reliable inside loops. 👍

To clear a bit you need a mask with that position OFF and all others ON. The NOT operator (~) flips every bit of your simple mask.

AND the number with the inverted mask to force that bit to 0 while keeping the rest. This is how you clear a single bit.

XOR with a single-bit mask flips that position: 0 becomes 1 and 1 becomes 0. This toggle is the cleanest one-liner of the three.

AND the number with a single-bit mask. If the result is nonzero, that bit is set; if it is zero, the bit is off.

Shift the number right to bring your target bit to the bottom, then AND with 1. You get exactly the bit value, 0 or 1.

Setting, clearing, and toggling let you store many on or off flags inside one integer. That is the heart of compact bitmask state in contests.

Bit positions start at 0, so bit k lives at value 1 shifted left by k. Mixing up the index is the most common beginner bug here.

Pick the right operation for clearing a bit.

OR sets, AND with NOT clears, and XOR toggles a single bit. Master these three masks and you control any bit you like. 🎉