a simple question

[zl2k]

hi,
In a function of a class, I have a unsigned long A (65535) and a
double B (0-1) and when I calculate a*b I should get a double 0-65535.
But, I get an unreasonable large value (e+9) if doing "cout<<A*B;".
However, I get the correct value if doing "cout<<B*A;" or
"cout<<(double)A*B". Can someone explain what's wrong with the code?
If I take the piece out of the function and run it separately, both
A*B and B*A give the same correct result. Thanks for the comments.
zl2k

 

[Greg Herlihy]

hi,
In a function of a class, I have a unsigned long A (65535) and a
double B (0-1) and when I calculate a*b I should get a double 0-65535.
But, I get an unreasonable large value (e+9) if doing "cout<<A*B;".
However, I get the correct value if doing "cout<<B*A;" or
"cout<<(double)A*B". Can someone explain what's wrong with the code?

What code?

Greg

 

[Jim Langston]

hi,
In a function of a class, I have a unsigned long A (65535) and a
double B (0-1) and when I calculate a*b I should get a double 0-65535.
But, I get an unreasonable large value (e+9) if doing "cout<<A*B;".
However, I get the correct value if doing "cout<<B*A;" or
"cout<<(double)A*B". Can someone explain what's wrong with the code?
If I take the piece out of the function and run it separately, both
A*B and B*A give the same correct result. Thanks for the comments.
zl2k

Following program outputs:
32767.5
32767.5
32767.5

which is not what you describe.

Please show the code you are doing.

#include <iostream>
#include <string>

int main()
{
unsigned long A = 65535;
double B = 0.5;

std::cout << A * B << "\n";
std::cout << B * A << "\n";
std::cout << double(A) * B << "\n";

std::string wait;
std::getline( std::cin, wait );

}