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); 
}

• slepic: Hi, please include the main class/function and imports so that people can just copy your code and compile it without having to add anything to it.
• elmer007: @slepic Using .NET 6, the code as-is can be copied/pasted and run without any changes. I just launched a new project in VS, copied the code in the question, and ran it without issue. Line 1 is the first Console.WriteLine(), and the last line in the file is line 28, the closing brace of the final else if block. If OP is just starting with C#, it's likely that their file only contains what's shown in the question (and perhaps are not aware of namespaces, public static void Main etc.)

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;
}

• CompuChip: And while you're at it (it being "error handling") you may want to check that numberTwo is not zero when dividing.
• minnmass: As an alternative for the try/catch, you could also use double.TryParse. That would also simplify making the app loop until valid numbers are entered.
• sbottingota: @CompuChip, is this what you mean (I have added a section).
• H. Pauwelyn: Don't use try catch for converting numbers. Use double.TryParse instead. Try catch will have an impact on performance in duration each time the users enters an invalid number.
• akinuri: Also, there's no need to duplicate operations (WriteLine). Logic should only modify the data. So create a result variable. Modify it as many times as you need. Print it once.