'conversion' : conversion from 'type1' to 'type2', signed/unsigned mismatch
You attempted to convert a signed const that has a negative value to an unsigned.
The following code shows this warning:
const int i = -1;
unsigned int j = i; // warning C4245
const int k = 1;
unsigned int l = k; // okay
int m = -1;
unsigned int n = m; // okay