#include <iostream>
using namespace std;

int main() {
  constexpr double cm_per_inch = 2.54;
  double length = 1;
  char unit = ' ';

  cout << "Please enter a length followed by a unit (c or i):\n";
  cin >> length >> unit;

  if(unit == 'i') {
    cout << length << "in == " << length * cm_per_inch << "cm\n";
  } else if(unit == 'c') {
    cout << length << "cm == " << length / cm_per_inch << "in\n";
  } else {
    cout << "ERROR! " << unit << " is not a valid unit. Use i for inches or c for centimeters.\n";
  }
}