Want to Call a method from the Main twice and display the two outputs

Question

Im wanting to call a method twice where the user has to input two positive doubles. I then want those to be returned to the main() and displayed. I'm unsure how to call the method from the main as I have only done this using methods with 1 type of input.

       public static void Main(string[] args)
       {
        double costLitres = VolumeAndCost();
        }
        public static double VolumeAndCost(double costLitres)
       {
        double litresOfFuel;
        double costOfFuel;
        Console.WriteLine("Please Enter The Number Of Litres Of Full Put Into Car.");

        litresOfFuel = Convert.ToDouble(Console.ReadLine());
    
        if (litresOfFuel > 0)

        {
            return litresOfFuel;
        }

        else

        {
            Console.WriteLine("Please enter a positive value.");
            litresOfFuel = Convert.ToDouble(Console.ReadLine());

        }

        Console.WriteLine("Please Enter The Cost Of The Fuel In Dollars And Cents.");
        costOfFuel = Convert.ToDouble(Console.ReadLine());

        if (costOfFuel > 0)
        {
            return costOfFuel;
        }
        else
        {
            Console.WriteLine("Please enter a positive value.");
            costOfFuel = Convert.ToDouble(Console.ReadLine());
            return costOfFuel;

        }

Answer 1

I think the VolumeAndCost() is too complex to be able to reuse. It does mutiple things. Try to separate them in much simplere functions which can be reused.

About the example:

For example the AskPositiveDouble(); method will loop util the criterea "is double and positive". Otherwise it will ask again. In future, there will be a situation that the user should be able to cancel this all. That will be the next step. (double? liters and when it returns a default 0 in this case)_, you can stop the program.

VolumeAndCost is not that special, but using a separate method can have some benefits, that where you want to calculate the price, it's on one spot of the code. (for example if you want to add tax, later you only need to change that method.)

Tip: Try to avoid using Convert.ToDouble(). When the value is not a double, it will raise an exception. You should avoid exceptions as much as possible; It disrupts the good flow in your application. double.TryParse() is here to help. It returns false when the string doesn't contain a valid double value and when it returns true, the value variable will hold it's value.

Here is the example code:

using System;

public class Program
{

    public static void Main()
    {
        // ask the liters
        Console.WriteLine("Please Enter The Number Of Litres Of Full Put Into Car.");
        double liters = AskPositiveDouble();

        // ask the cost per liter
        Console.WriteLine("Please Enter The Cost Of The Fuel In Dollars And Cents.");
        double costOfFuel = AskPositiveDouble();

        // calculate costs
        double cost = CalculateCosts(liters, costOfFuel);

        // output to the screen
        Console.WriteLine($"The price will be {cost:f2}");
    }

    private static double AskPositiveDouble()
    {
        // loop
        while(true)
        {
            // if the user enters a double value, it continues checking.
            string input = Console.ReadLine();
            if(double.TryParse(input, out var value))
            {
                // if the value is positive, return that value
                if(value > 0)
                    return value;

                // otherwise show this information and repeat the input.
                Console.WriteLine("Please enter a positive value.");
            }
        }
    }

    private static double CalculateCosts(double liters, double costOfFuel)
    {
        // calculation.
        return liters * costOfFuel;
    }
}