Subtraction without minus sign in C

Question

How can I subtract two integers in C without the - operator?

Answer 1

Iff:

1. The Minuend is greater or equal to 0, or
2. The Subtrahend is greater or equal to 0, or
3. The Subtrahend and the Minuend are less than 0

multiply the Minuend by -1 and add the result to the Subtrahend:

SUB + (MIN * -1)

Else multiply the Minuend by 1 and add the result to the Subtrahend.

SUB + (MIN * 1)

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Example (Try it online):

#include 

int subtract (int a, int b)
{
    if ( a >= 0 || b >= 0 || ( a < 0 && b < 0 ) )
    {
        return a + (b * -1);
    }

    return a + (b * 1); 
}

int main (void)
{
    int x = -1;
    int y = -5;
    printf("%d - %d = %d", x, y, subtract(x, y) );
}

Output:

-1 - -5 = 4