need help with calculator

Code:

`// my calculator.cpp : Defines the entry point for the console application.`

//

#include <iostream>

using namespace std;

int main()

{

int first, second, todo;

cout << "This is a calculator for basic math functions between two integers.\n";

cout << "What would you like to do?\n1: Addition\n2: Subtraction\n3: multiplication\n4: Division\n";

cin >> todo;

if (todo > 4)

cout << "Please enter a number 1 - 4";

cout << endl;

cout << "Please insert the two integers you would like to use: ";

cin >> first;

cin >> second;

if (todo == 1)

cout << "The answer is: " << first + second << endl;

if (todo == 2)

cout << "The answer is: " << first - second << endl;

if (todo == 3)

cout << "The answer is: " << first * second << endl;

if (todo == 4)

cout << "The answer is: " << first / second << " With a remainder of " << first % second << endl;

system("pause");

return 0;

}

when the user inputs an incorrect number for addition subtraction etc. it says "please enter a number 1 - 4" but then it just goes to the next step, how can i fix this?