Printable View
I have a mathematical problem with C. For some reason the variables x and y in the code below are not exactly equal all of the time. I believe that the problem has to do with casting. How, exactly do I cast the equations for x and y so that they are always equal?
Code:long x, y, w;
double a, b;
x = a*w/b+0.5;
What conditions make these not equal? Does it have to do with overflow?
I edited the first post. I misunderstood my problem. I still suspect though that I have a problem with casting.
regarding your post. My variables are b = 350, 3 < a < 500, and 10 < w < 200,000.
Sorry, but there's really nothing you can do.
double and float are just approximations, so most mathematical truisms don't apply.
Case in point:
Code:#include <iostream>
int main (void) {
double a = 9.95;
double b = 1;
long x;
x = a/b + .05;
std::cout << x << '\n'; // 9
a *= 10;
b *= 10;
x = a/b + .05;
std::cout << x << '\n'; // 10
return 0;
}
Both are 10 with your code compiled with gcc on a 32-bit machine.
Except where they aren't both 10 on a 32-bit machine compiled with gcc in either C (with necessary modifications) or C++.Quote:
Originally Posted by SKeane
Your mileage may vary. Optomization, for example, will change the results. Typically, (int) (9.95 + 0.05) == 9 is a really safe bet.Quote:
Originally Posted by SKeane
Funny, I get 10.000000.Quote:
Originally Posted by QuestionC