What is the result of ~0 in C?

Every bit becomes 1, which in two's complement is −1 (e.g. 0xFFFFFFFF for a 32-bit int).

~0 = 0xFFFFFFFF (for 32-bit int)
   = -1 in two's complement

Why:

• 0 = all zeros: 00000000...
• ~0 = all ones: 11111111...
• In two's complement, all 1s = -1

Useful for: Creating bit masks, representing "no value" in unsigned contexts.