Calculator in C++

Calculator.cpp

#include <iostream>
using namespace std;

float a, b, r;
char key;
string spr = "==========================\n";
int main();

void reset()
{
	system("sleep 2");
    system("cls");
    main();
}


float mul(float x, float y)
{
    return x * y;
}

float div(float x, float y)
{
    return x / y;
}

float add(float x, float y)
{
    return x + y;
}

float sub(float x, float y)
{
    return x - y;
}

int main() 
{
	cout << spr << "App Name: Calculator\nCoded by: Zephio\nLanguage: C++\n" << spr << "(*) Mul\n(/) Div\n(+) Add\n(-) Sub\n" << spr << "Choose Operator: ";
	cin >> key;
	cout << spr;
    cout << "Enter Value A: ";
    cin >> a;
    cout << "Enter Value B: ";
    cin >> b;
	
switch (key)
{
do
{
// mul
case char(0x2a):
    r = mul(a, b);
    cout << "Result: " << r << endl;
    reset();
break;
// div
case char(0x2f):
    r = div(a, b);
    cout << "Result: " << r << endl;
    reset();
break;
// add
case char(0x2b):
    r = add(a, b);
    cout << "Result: " << r << endl;
    reset();
break;
// sub
case char(0x2d):
    r = sub(a, b);
    cout << "Result: " << r << endl;
    reset();
break;
default:
    cout << "Invalid choice"  << endl;
    reset();
}
while (key != 0);
}
    return 0;
}