How to make simple calculator in C#

using System;
namespace calcualtor
{
class calculator
{
static void Main(string[] args)
{
int n1,n2,n3;
Console.Write("Enter first number = ");
n1 = Convert.ToInt32(Console.ReadLine());
Console.Write("Enter second number = ");
n2 = Convert.ToInt32(Console.ReadLine());
char a; // for switch
Console.Write("choose mathematical expression \n + , - , * , /\n");
a = Convert.ToChar(Console.ReadLine());
switch (a)
{
case '+':
n3 = n1 + n2;
Console.WriteLine($"{n1} + {n2} = {n3}");

break;
case '-':
n3 = n1 - n2;
Console.WriteLine($"{n1} - {n2} = {n3}");
break;
case '*':
n3 = n1 * n2;
Console.WriteLine($"{n1} * {n2} = {n3}");
break;
case '/':
n3 = n1 / n2;
Console.WriteLine($"{n1} / {n2} = {n3}");
break;
}
Console.ReadKey();
}
}
}