decimal places and Pow function in c++

Question

Most likely a really simple question, please keep any answers easy to understand I'm still quite new at this:

I'm making a little app, and I need to use powers for a couple of calculations. After a little research I found the pow function in cmath, and have had a play. In the end i came up with this snipped, which works:

#include <iostream>
#include <cmath>
using namespace std;

int main ()
{
    float dummy2, test(6.65);
    dummy2 = (float) pow((float) 3.57, test);
    cout << dummy2;

    return 0; 
}

and it returns the correct answer (4734.17), but only to two decimal places. I want 5 decimal places preferably.

What did I do wrong here? Am I using the wrong data type (floats)? Or is it a limit of whatever is in the pow function to using only 2dp?

I could, if it came to it just define constants with the values i want, since it's only going to be 4 or 5 sums that I need this precision on, but if it's possible to have the program calculate it that would be great.

Thanks

Answer 1

For a better precision you should use double. Doubles has 15 digits of precision against 7 for floats.

Answer 2

Google is your friend. These results and these as well have what you want, namely that you need to use setprecision() as a cout parameter.

Answer 3

I would do as fbinder says, and use Doubles for greater precision. To solve your problem, you have two options, C-style and C++ style.

C-Style

#include <cstdio>
printf("%.5f", dummy2);

C++ Style

#include <iomanip>
std::cout << setprecision(5) << dummy2 << std::endl;

OR

std::cout.precision(5);
std::cout << dummy2 << std::endl;
// continue to use cout to output 5 decimal places