C# code executes even when variable not assigned

Question

As you can probably tell from my question, I am very new to coding. I am trying to make a calculator that computes some formulas that are used in physics. However, the code runs the formula before the user has time to enter a value for A, in this example at least. Here is the example:

case "f = ma":
    Console.WriteLine("Type the value for M in KG:");
    var FM = Console.Read();
    Console.WriteLine("Type the value for A in M/S:");
    var FA = Console.Read();
    var FMARes = FM * FA;
    Console.WriteLine("Your answer (in Newtowns) is " + FMARes);
break;

How am I able to check whether a value has been assigned to the variable A, and only run the formula after the variable has an assigned value? Thanks.

Answer 1

You need to use ReadLine instead of Read. You also need to do another ReadLine at the bottom so the user can see the result. And...you should validate that the user entered a valid number. This could be refactored a bit to avoid duplicate code - etc. - but see if this works for you! Good luck!!

    static void Main(string[] args)
    {
        double fm;
        double fa;

        // Use ReadLine instead of Read 
        Console.WriteLine("Type the value for M in KG:");
        var input = Console.ReadLine();

        // Now you need to cast it to a double - 
        // -- but only if the user entered a valid number 
        if (!double.TryParse(input, out fm))
        {
            Console.WriteLine("Please enter a valid number for M");
            Console.ReadLine(); 
            return; 
        }

        Console.WriteLine("Type the value for A in M/S:");
        input = Console.ReadLine();
        if (!double.TryParse(input, out fa))
        {
            Console.WriteLine("Please enter a valid number for A");
            Console.ReadLine();
            return; 
        }

        // Now we have valid values for fa and fm 
        // It's a better programming practice to use the string format 
        // intead of + here... 
        Console.WriteLine($"Your answer (in Newtowns) is {fm * fa}");

        // You need another read here or the program will just exit
        Console.WriteLine("Press Enter to end the program");
        Console.ReadLine(); 
    }