C : Modulus operator on unsigned int gives unexpected output

Question

#include 

main() {
    unsigned a = -20;
    unsigned b = 10;
    printf(\"%d\\n\", (a % b));
    printf(\"%d\\n\", (-20 % 10));
}

Output:
6
0
         


        

Answer 1

unsigned int can hold values from 0 to UINT_MAX, no negative values. So -20 is converted to -20 + UINT_MAX + 1.

On your system:

(-20 + UINT_MAX + 1) % 10 != -20 % 10