methods - C# Value unitialized

Question

I have a problem that I have been trying to sort out for quite a while now but I just can't wrap my head around it. I have two double variables that are initialized. Obviously, I get an error for that because they should have a value. However, the only value I could set it to is 0. The issue with that is, if I set the value to 0, my program does not run correctly and the output of my program becomes 0 too.

Error: Local variable 'userSalary' might not be initialized before accessing

I am still kind of learning the ways of methods, parameters, and arguments.

class Program
{
    static void Main(string[] args)
    {
        double userSalary;
        double leftOver;
        AskQuestion(userSalary);
        CalculateTax(userSalary, leftOver);
    }
    
    static void AskQuestion(double userSalary)
    {
        Console.WriteLine("What is annual your salary?");
        userSalary = Convert.ToDouble(Console.ReadLine());

    }

    static void CalculateTax(double userSalary, double leftOver)
    {
        if (userSalary <= 14_000) //10%
        {
            Console.WriteLine("You are in Tax Category 1. 10% of your Salary goes to the state!");
            Console.WriteLine("Calculating Salary...");
            Thread.Sleep(500);
            leftOver = userSalary - (userSalary * 10 / 100);
            Console.WriteLine("Your Salary after taxation is: $" + leftOver);
        }
    }

}

Answer 1

You have multiple problems here.

Firstly, your "Error: Local variable 'userSalary' might not be initialized before accessing" problem:

While fields (class-level variables) are initialized to their default values when constructing a class, method variables are not initialized. To do so, you would need to assign a value to them. For example:

double userSalary = 0;
double leftOver = 0;

The next problem you have is that all variables are passed by value (i.e. a copy is made) and not by reference. Note that this is not to say that the types being passed are not reference types, but that the pointer the variable represents is passed as a copy. You can read more on that here.

What this means for you is that, while AskQuestion changes its own userSalary argument variable, it doesn't change the calling method's variable. One way to solve this is to use the ref or out keywords. (ref is used where the variable is already initialized but the method changes it, out is used where the method initializes the variable). More on that here.

So you could write your code like this:

static void AskQuestion(out double userSalary)

And then call it like so:

double userSalary;
AskQuestion(out userSalary);

or simply:

AskQuestion(out double userSalary);

Though a better approach is to have the method simply return the result. We'll also remove the leftOver argument from CalculateTax as that isn't used anywhere:

_{Note : You should always use TryParse Style methods to validate user input}

static double AskQuestion()
{
   double userSalary;
   Console.WriteLine("What is annual your salary?");
   // simple validation loop
   while (!double.TryParse(Console.ReadLine(), out userSalary))
      Console.WriteLine("You had one job... What is annual your salary?");
   return userSalary;
}

static void CalculateTax(double userSalary)
{
    if (userSalary <= 14_000) //10%
    {
        Console.WriteLine("You are in Tax Category 1. 10% of your Salary goes to the state!");
        Console.WriteLine("Calculating Salary...");
        Thread.Sleep(500);
        double leftOver = userSalary - (userSalary * 10 / 100);
        Console.WriteLine("Your Salary after taxation is: $" + leftOver);
    }
}

And then initialize userSalary and call CalculateTax like so:

userSalary = AskQuestion();
CalculateTax(userSalary);