How to 'cout' the correct number of decimal places of a double value?

Question

I need help on keeping the precision of a double. If I assign a literal to a double, the actual value was truncated.

int main() {
    double x =         


        

Answer 1

Due to the fact the float and double are internally stored in binary, the literal 7.40200133400 actually stands for the number 7.40200133400000037653398976544849574565887451171875

...so how much precision do you really want? :-)

#include     
int main()
{
    double x = 7.40200133400;
    std::cout << std::setprecision(51) << x << "\n";
}

And yes, this program really prints 7.40200133400000037653398976544849574565887451171875!