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

constexpr double pi = 4*atan(1); // will be in read-only data section

int main( void)
{
  cout << pi << '\n';
}

/* sample run:

$ alias GGG
g++ -std=c++11 -pedantic -Wall
$ GGG PI.cc
$ ./a.out
3.14159
$

*/