Question

With this code:

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

//Functions
int power(int base,int exp);
double energy(int z, int n);

//Main
int main() {


    const double E0(13.6),hce(1.24E-6),e(1.6E-19);
    int n1,n2,z;
    double E;
    cout << "**************************************" << endl;
    cout << "Welcome to the energy level calculator\n" << endl;
    cout << "Please enter the atomic number, z: " << endl;
    cin >> z;   //Ask for z
    cout << "Please enter n for the initial energy level: " << endl;
    cin >> n1;  //Ask for n1
    cout << "Please enter n for the final energy level: " << endl;
    cin >> n2;  //Ask for n2

    while(cin.fail()||z<1||n1<1||n2<1){
        cout << "\n\n\n\n\nPlease enter non-zero integers only, try again\n\n\n\n\n\n" << endl;
        cout << "**************************************" << endl;
        cin.clear();
        cin.ignore();
        cout << "Please enter the atomic number, z: " << endl;
        cin >> z;   //Ask for z
        cout << "Please enter n for the initial energy level: " << endl;
        cin >> n1;  //Ask for n1
        cout << "Please enter n for the final energy level: " << endl;
        cin >> n2;  //Ask for n2
    }
    etc...

The program is only allowed to accept Integers
If i enter a decimal, such as 1.2 the program rejects the 1. but uses the 2 as z when it should be asking for input from the keyboard?
Can anyone help?

Answer 1

Since you asked for an explanation, when you enter 1.2

cin >> z;   //Successfully reads '1' into 'z'

cin >> n1;  //Fails to read '.' into 'n1'. '.' remains the first character in the stream.

cin >> n2;  //Fails to read '.' into 'n2'. '.' remains the first character in the stream.

You then loop back to the beginning of your loop.

cin.clear(); //clears the fail flag from the two previous failed inputs
cin.ignore(); // ignores the '.'

cin >> z;   //Reads '2' into 'z'. The stream is now empty.

The program then blocks on cin >> n1 waiting for more characters to be placed in the stream.

After each input, you should see if the input failed.

cin>>n1;
if(cin.fail())
   cin.ignore();