Why do I get errors when using unsigned integers in an expression with C++?
- by neuviemeporte
Given the following piece of (pseudo-C++) code:
float x=100, a=0.1;
unsigned int height = 63, width = 63;
unsigned int hw=31;
for (int row=0; row < height; ++row)
{
for (int col=0; col < width; ++col)
{
float foo = x + col - hw + a * (col - hw);
cout << foo << " ";
}
cout << endl;
}
The values of foo are screwed up for half of the array, in places where (col - hw) is negative. I figured because col is int and comes first, that this part of the expression is converted to int and becomes negative. Unfortunately, apparently it doesn't, I get an overflow of an unsigned value and I've no idea why.
How should I resolve this problem? Use casts for the whole or part of the expression? What type of casts (C-style or static_cast<...)? Is there any overhead to using casts (I need this to work fast!)?
EDIT: I changed all my unsigned ints to regular ones, but I'm still wondering why I got that overflow in this situation.
