Improved TSHIRT Program

#include <iostream>
#include <cstdlib>

    /*
      Programmer: Bryan Virgil
      Date:       10 04 2017
      Description:    Tshirt company is giving the following discounts
                        1..5   --> 0% discounts
                        6..10  --> 10% discounts
                        10+    --> 25% discounts*/

using namespace std;

const int  TSHIRT_PRICE = 10;
const double DISCOUNT_5_PCT = 0.05;
const double DISCOUNT_10_PCT = 0.10;
const double DISCOUNT_15_PCT = 0.15;
const double DISCOUNT_20_PCT = 0.20;
const double DISCOUNT_25_PCT = 0.25;

int main()
{

    int numTShirts; // used to hold number of thisrts purchased
    double discount = 0;


    cout << "How many T-Shirts did you purchase:";
    cin >> numTShirts;
    if (cin.fail())
    {
        cout << "Wrong data type, please run the program" << endl;
    }
    else
    {
        if (numTShirts < 1)
        {
            cout << "Invalid quantity, please run the program again" << endl;
            cout << "Exiting..." << endl;
          //  exit(EXIT_FAILURE);
          // use else statement to get rid of EXIT_FAILURE
        }
        // get rid of the exit and implement the else part
       // else

       else
       switch(numTShirts)
       {
        case 1 ... 5:
            totalPrie - numTShirts * TSHIRT_PRICE + discount;
            cout << "You get 0% discount" << endl;
           break;
        case 6 ... 10:
           cout << "You get 5% discount" << endl;
           subtotal = numTShirts * TSHIRT_PRICE;
           discount = subTotal * DISCOUNT_5_PCT;
           totalPrice = subTotal - discount;
            break;
        case 11 ... 20:
           cout << "You get 10% discount" << endl;
            subtotal = numTShirts * TSHIRT_PRICE;
           discount = subTotal * DISCOUNT_10_PCT;
           totalPrice = subTotal - discount;
            break;
        case 21 ... 50:
           cout << "You get 15% discount" << endl;
            subtotal = numTShirts * TSHIRT_PRICE;
           discount = subTotal * DISCOUNT_15_PCT;
           totalPrice = subTotal - discount;
            break;
        case 51 ... 100:
           cout << "You get 20% discount" << endl;
            subtotal = numTShirts * TSHIRT_PRICE;
           discount = subTotal * DISCOUNT_20_PCT;
           totalPrice = subTotal - discount;
            break;
        default:
             cout << "Call for discount" << endl;
       }

       cout << "You purchased: " << numTShirts << endl;
       cout << "Your subtotal was $: " << subTotal << endl;
       cout << "Your discount was $: " << discount << endl;
       cout << "Your total price was $ " << totalPrice << endl;
       cout << "" <<
    }
    return 0;
}