c - Subtracting two numbers without using '-' operator - Stack Overflow

int add(int a, int b) {
    while (a) {
        a = (a & b) << 1;
        b = a^b;
    }
    return b;
}

int sub(int a, int b) // add a with b's 2's complement.
{
    return (add(a, add(~b, 1)));
}

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