C++ Program crashes/infinite looping if a letter is inputted as an answer instead of a number

Question

Sorry if I fail to be clear enough or make any mistakes,

I am taking a C++ course so please go easy one me. So my code runs without errors when complied but the problem I have is the program goes into an infinite loop if you press a letter in the menu option and in your input for your answer.

Why is this and what can I do to make it run normally?

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

int main()
{
   int num1,      
   num2,        
   choice,        
   studentAnswer, 
   correctAnswer;

  srand(time(0));
  do
  {  
    cout << "\n-----------------------------------\n"
         << "           Math Tutor\n"
         << "            M E N U\n"
         << "-----------------------------------\n";
    cout << "1. Addition problem\n";
    cout << "2. Subtraction problem\n";
    cout << "3. Multiplication problem\n";
    cout << "4. Division problem\n";
    cout << "5. Quit this program\n";
    cout << "------------------------------\n";
    cout << "Enter your choice (1-5): ";
    cin >> choice;
    while (choice < 1 || choice > 5)
    {
        cout << "The valid choices are 1, 2, 3, "
            << "4, and 5. Please choose: ";
        cin >> choice;
    }
    switch (choice)
    {
    case 1:
        num1 = 1 + rand() % 500;
        num2 = 1 + rand() % 500;
        correctAnswer = num1 + num2;
        cout << "\n\n";
        cout << "  " << setw(4) << num1 << endl;
        cout << " +" << setw(4) << num2 << endl;
        cout << "  " << "----" << endl;
        cout << "   ";
        break;
    case 2:
        num1 = 1 + rand() % 999;
        num2 = 1 + rand() % 999;
        while (num2 > num1)
            num2 = 1 + rand() % 999;
        correctAnswer = num1 - num2;
        cout << "\n\n";
        cout << "  " << setw(4) << num1 << endl;
        cout << " -" << setw(4) << num2 << endl;
        cout << "  " << "----" << endl;
        cout << "   ";
        break;
    case 3:  
        num1 = 1 + rand() % 100;
        num2 = 1 + rand() % 9;
        correctAnswer = num1 * num2;
        cout << "\n\n";
        cout << "  " << setw(4) << num1 << endl;
        cout << " *" << setw(4) << num2 << endl;
        cout << "  " << "----" << endl;
        cout << "   ";
        break;
    case 4:
        num2 = 1 + rand() % 9;
        num1 = num2 * (rand() % 50 + 1);
        correctAnswer = num1 / num2;
        cout << "\n\n";
        cout << "  " << num1 << " / " << num2 << " = ";
        break;
    case 5:  
        cout << "Thank you for using Math Tutor.\n\n";
        break;
    }
    if (choice >= 1 && choice <= 4)
    {
        cin >> studentAnswer;
        if (studentAnswer == correctAnswer)
            cout << "\n\nCongratulations! That's right.\n\n";
        else
            cout << "\n\nSorry, the correct answer is " << correctAnswer
            << ".\n\n";
    }
  } while (choice != 5);  
  return 0;
}