#include <iostream>
#include <cmath>
#include <iomanip>
#include <string>

using namespace std;

float energy(int n, float m, float L);

int main () {

float Me = 9.109E-31, Mp = 1.67E-27;
double h = 6.626E-34, U;
string name;

int Particle = 0;
char P, E;

while ((Particle != 'P') || (Particle != 'E')) {

cout << "Please enter 'P' to check Proton energy or 'E' for Electron energy." << endl;
if (!(cin >> Particle)) {
cin.clear();
cin.ignore(255,'\n');
}
if ((Particle != 'P') || (Particle != 'E')) {
cout << "The character you have entered is invalid. Please enter 'P' or 'E'." << endl;
}

}

float State = 0;

while (( State < 1) || (State/(int)State !=1)){

cout << "Please enter the energy state" << endl;
if (!(cin >> State)) {
cin.clear();
cin.ignore(255,'\n');
}
if (( State < 1) || (State/(int)State !=1));
cout << "Invalid Energy state. Please enter a positive integer for this value." << endl;
}

}


switch (Particle) {
case 'P' :
name = "Proton";
L = 1E-14;
m = Mp;
U = energy((int)State, m, L);
break;
case 'E' :
name = "Electron" ;
L = 1E-10;
m = Me;
U = energy((int)State, m, L);
break;


}

cout << "At n = " << (int)State << " the energy of the " << name << " is " << U/(1.602E-19) << " eV." << endl;
return 0;



float energy(int n, float m, float L) {
return (pow(n,2)*pow(h,2)/(8*m*pow(L,2));
}