Well, it calculates, it just won't loop, or exit right. . .
I've tried a lot of things, I just don't know why it won't work right. So please help me.
Code:
#include <iostream>

	int addition ( int x, int y )
	{
		return x + y;
	}

	int subtraction ( int x, int y )
	{
		return x - y;
	}

	int multiplication ( int x, int y )
	{
		return x * y;
	}

	int division ( int x, int y )
	{
		return x / y;
	}

using namespace std;

int add();
int sub();
int mul();
int div();
int main()
{
	int input, z;
	z = 0;
	do
	{
		cout<<"1. Add\n2. Subtract\n3. Multiply\n4. Divide\nE. Exit\nEnter your choice: ";
		cin>> input;
			switch ( input ) {

			case 1:
				add();
			break;

			case 2:
				sub();
			break;

			case 3:
				mul();
			break;

			case 4:
				div();
			break;

			case 'E':
				( z + 1 );
			break;

			default:
				cout<<"Error: Unknown Input\n";
			break;
			}
		return 0;
    } while ( z != 1 );
}
	int sub(){
	int x, y;
		cout<<"Enter the first number to subtract: ";
			cin>> x;
			cin.ignore();
		cout<<"Enter the second number to subtract: ";
			cin>> y;
			cin.ignore();
		cout<<"The difference is: "<<subtraction ( x , y );
		cout<<"\n";
		return 0;
	}

	int add(){
	int x, y;
		cout<<"Enter the first number to add: ";
			cin>> x;
			cin.ignore();
		cout<<"Enter the second number to add: ";
			cin>> y;
			cin.ignore();
		cout<<"The sum is: "<<addition ( x, y );
		cout<<"\n";
		return 0;
	}

	int mul(){
	int x, y;
		cout<<"Enter the first number to be multiplied: ";
			cin>> x;
			cin.ignore();
		cout<<"Enter the second number to be multiplied: ";
			cin>> y;
			cin.ignore();
		cout<<"The product is: "<<multiplication ( x, y );
		cout<<"\n";
		return 0;
	}

	int div(){
	int x, y;
		cout<<"Enter the first number to be divided: ";
			cin>> x;
			cin.ignore();
		cout<<"Enter the second number to be divided: ";
			cin>> y;
			cin.ignore();
		cout<<"The quotiant is: "<<division ( x, y );
		cout<<"\n";
		return 0;
	}
When I make Exit '5' instead of 'E' it works, but it says, "Press any key to continue." I have tried the 'while' loop, but when I do it I get a black screen. I don't know why it's not working, so please help me with this.