Basic C# Calculator

Question

I am a beginner programmer, I decided to make this calculator program to test my knowledge on basic C# syntax, the code executes as intended, however I would like to shorten it to be more concise.

Console.WriteLine("Please select your first number: ");

double numberOne = Convert.ToDouble(Console.ReadLine());

Console.WriteLine("Please select your second number: ");

double numberTwo = Convert.ToDouble(Console.ReadLine());

Console.WriteLine("Please choose the operation: "); 

var userInput = Console.ReadLine(); 

if (userInput == "+") 
{
    Console.WriteLine(numberOne + numberTwo);
}
else if (userInput == "-")
{
    Console.WriteLine(numberOne - numberTwo);
}
else if (userInput == "*")
{
    Console.WriteLine(numberOne * numberTwo);
}
else if (userInput == "/")
{
    Console.WriteLine(numberOne / numberTwo); 
}

Answer 1

Your code is good, but there are a few improvements that you could make.

Determining what operation your user wants.

Instead of using if/else, I'd probably use a switch/case statement:

switch userInput
{
    case "+":
        Console.WriteLine(numberOne + numberTwo);
        break;
    case "-":
        Console.WriteLine(numberOne - numberTwo);
        break;
    case "*":
        Console.WriteLine(numberOne * numberTwo);
        break;
    case "/":
        Console.WriteLine(numberOne / numberTwo);
        break;
}

Error handling with user inputs

I'd probably also put a default clause, just in case your user doesn't enter one of + - * /:

switch userInput
{
    ...
    default:
        Console.WriteLine("Sorry, unknown operation.");
        break;
}

I would also use a try/catch block for figuring out what numberOne and numberTwo are:

try
{
    Console.WriteLine("Please select your first number: ");
    double numberOne = Convert.ToDouble(Console.ReadLine());
    
    Console.WriteLine("Please select your second number: ");
    double numberTwo = Convert.ToDouble(Console.ReadLine());
}
catch (FormatException)
{
    Console.WriteLine("Sorry, invalid number."); 
}

You might also want to check whether numberTwo is not zero when dividing:

switch userInput
{
    ...
    case "/":
        if numberTwo == 0
        {
            Console.WriteLine("Sorry, cannot divide by zero.");
        }
        else
        {
            Console.WriteLine(numberOne / numberTwo);
        }

        break;
}