You sent me to the standard to check ;) It does specify 0 or 1, but you should be good:

3 The == (equal to) and != (not equal to) operators are analogous to the relational
operators except for their lower precedence.91) Each of the operators yields 1 if the
specified relation is true and 0 if it is false. The result has type int. For any pair of
operands, exactly one of the relations is true.