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

std::cout << std::setprecision(8) << x;

Note that setprecision is persistent and all next floats you print will be printed with that precision, until you change it to a different value. If that's a problem and you want to work around that, you can use a proxy stringstream object:

std::stringstream s;
s << std::setprecision(8) << x;
std::cout << s.str();

For more info on iostream formatting, check out the Input/output manipulators section in cppreference.