#include <iostream>         /// cout
#include <iomanip>          /// setprecision()

using namespace std;


int main()
{
    cout << "cout.precision()="
         << cout.precision() << " : "
         << 123.456 << endl;

    cout << "cout.precision()="
         << setprecision(4)
         << cout.precision() << " : "
         << 123.456 << endl;
}