Subtraction without minus sign in C

Question

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

Answer 1

• + No bit setting
• + Language independent
• + Can be adjusted for different number types (int, float, etc)
• - Almost certainly not your C homework answer (which is likely to be about bits)

Expand a-b:

a-b = a + (-b)
    = a + (-1).b

Manufacture -1:

float:             pi = asin(1.0);
(with    minusone_flt = sin(3.0/2.0*pi);
math.h)           or  = cos(pi)
                  or  = log10(0.1)
complex: minusone_cpx = (0,1)**2; // i squared
integer: minusone_int = 0; minusone_int--; // or convert one of the floats above