#include <iostream>   //for cout
#include <format>     //for format           c++ -std=c++20 precision.C
#include <cstdlib>    //for EXIT_SUCCESS;
using namespace std;

int main()
{
	double d {3.14159265358979};         //15 significant digits

	cout << d << "\n";                   //Output only 6 significant digits.

	cout << format("{:15}", d) << "\n";  //Output 15 significant digits.

	return EXIT_SUCCESS;
}