Very simple calculator with four basic operations using only if/else statements

I created a simple calculator with multiplication, division, addition, and subtraction. Is there a way to write it shorter? I am a beginner so I do not know much about programming other than if…else statements and different data types.

        Console.WriteLine("Welcome to the simple calculator! The four operators of this calculator are +, -, *(multiply), and /(divide)");
        Console.Write("Number: ");
        string number = Console.ReadLine();
        Console.Write("Second Number: ");
        string secondNumber = Console.ReadLine();
        Console.Write("Operator: ");
        string operatorType = Console.ReadLine();

        var numberConversion = Convert.ToInt64(number);
        var secondNumberConversion = Convert.ToInt64(secondNumber);
        var sum = numberConversion + secondNumberConversion; //Result of addition
        var difference = numberConversion - secondNumberConversion; //Result of subtraction
        var product = numberConversion * secondNumberConversion; //Result of multiplication
        var quotient = numberConversion / secondNumberConversion; //Result of division

        if (operatorType == "+")
        {
            Console.WriteLine(sum);
        } else if (operatorType == "-")
        {
            Console.WriteLine(difference);
        } else if (operatorType == "*")
        {
            Console.WriteLine(product);
        } else if (operatorType == "/")
        {
            Console.WriteLine(quotient);
        } else
        {
            Console.WriteLine("Please enter the correct operator");
        }

1. You need to check for input validity and have a mechanism for retry. Users can enter all sorts of things
2. Your variable names aren’t consistent. number and secondNumber. I would go with firstNumber and secondNumber in your scheme, but I would not use your scheme.
3. Your variable names are too verbose: secondNumberConversion. How about n1 and n2?
4. A simple, elegant, maintainable and extensible solution is to use a Dictionary.

Not addressing 1. here is my version:

Console.WriteLine("Welcome to the simple calculator!"
                  + " The four operators of this calculator are "
                  + "+, -, *(multiply), and /(divide)");

Console.Write("First Number: ");
Int64 n1 = Int64.Parse(Console.ReadLine());

Console.Write("Second Number: ");
Int64 n2 = Int64.Parse(Console.ReadLine());

Console.Write("Operator: ");
string operatorType = Console.ReadLine();

var operatorsFuncMap = new Dictionary<string, Func<Int64, Int64, Int64>> 
{
    {"+", (a, b) => a + b},
    {"-", (a, b) => a - b},
    {"*", (a, b) => a * b},
    {"/", (a, b) => a / b},
};

Console.WriteLine(operatorsFuncMap[operatorType](n1, n2));

Here’s how I would do it:

        Console.WriteLine("Welcome to the simple calculator! The four operators of this calculator are +, -, *(multiply), and /(divide)");
        Console.Write("Number: ");
        string number = Console.ReadLine();
        Console.Write("Second Number: ");
        string secondNumber = Console.ReadLine();
        Console.Write("Operator: ");
        string operatorType = Console.ReadLine();

        var numberConversion = Convert.ToInt64(number);
        var secondNumberConversion = Convert.ToInt64(secondNumber);

        switch (operatorType)
        {
            case "+":
                Console.WriteLine(numberConversion + secondNumberConversion);
                break;
            case "-":
                Console.WriteLine(numberConversion - secondNumberConversion);
                break;
            case "*":
                Console.WriteLine(numberConversion * secondNumberConversion);
                break;
            case "/":
                Console.WriteLine(numberConversion / secondNumberConversion);
                break;
            default:
                Console.WriteLine("Please enter the correct operator");
                break;
        }

More info here on switch: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/switch

I prefer using switch over a long If Then just because it’s easier to read.