Exercise: bit flags

A number flags stores a set of flags: flag number bit is on when bit number bit is 1. Write unsigned set_flag(unsigned flags, int bit) and unsigned clear_flag(unsigned flags, int bit): the first returns flags with that bit set to 1, the second with it cleared to 0, and every other bit stays the same. The third function, bool has_flag(unsigned flags, int bit), returns true if that bit is 1.

• set_flag(1u, 3) → 9u
• clear_flag(9u, 0) → 8u
• has_flag(2147483648u, 31) → true

Constraints: bit is from 0 to 31, and an unsigned takes 32 bits. If the bit is already set, set_flag returns flags unchanged; if it is already clear, clear_flag does the same.

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