Re: mixing signed and unsigned
Kai-Uwe Bux wrote:
John Harrison wrote:
I have a problem. I want to compare an integral value, n, against three
half open ranges as follows
[-A, 0) // range 1
[0, B) // range 2
[B, C} // range 3
Each range corresponds to a different outcome and if the integral value
isn't within any of the ranges, that's a fourth outcome. So far so easy,
the problem is that n is a signed quantity and A, B, C are unsigned
quantities. Apart from this obscure corner of my code this makes perfect
sense, so I don't want to change the signedness of anything.
How to I write these tests so that my code is reasonably understandable,
rather than a horrible mess of casts and compiler warnings?
One more point, of the unsigned quantity, only B is guaranteed small
enough that it could be safely cast to a signed integer.
What about:
#include <iostream>
int main ( void ) {
unsigned long A = 30;
unsigned long B = 20;
unsigned long C = 100;
long x = 0;
while ( std::cin >> x ) {
if ( x >= 0 ) {
if ( x < B ) {
std::cout << "range 2";
} else if ( x < C ) {
std::cout << "range 3";
} else {
std::cout << "above all ranges";
}
} else {
if ( ( -x ) <= A ) {
std::cout << "range 1";
} else {
std::cout << "below all ranges";
}
}
std::cout << '\n';
}
}
This only compares positive values. As long as the unsigned type is large
enough to represent the absolute values of the signed type, you will be
fine.
I thought of something like that, but two problems.
-x would overflow if x == std::numeric_limits<ptrdiff_t>::min()
"above all" and "below all" are the same outcome and I'd prefer not to
write the same code twice
john
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