C# Pass an integer variable with an optional default value

Question

class Program
{
    static void Main(string[] args)
    {
        WriteLine("What is the radius of your circle: ");
        WriteLine("The area of your circle is: " + 
            circleArea(Double.Parse(ReadLine())).ToString());
        ReadKey();
    }

    static double circleArea(double radius = 5.00)
    {            
        return Math.PI * (radius * radius);
    }
}

I thought I had it set up correctly; however, I receive an error of System.FormatException: 'Input string was not in a correct format. on the line WriteLine("The area of your circle is: " + circleArea(Double.Parse(ReadLine())).ToString()); when no value is entered. I would like it to have a default value of 2. Thanks.

Answer 1

Your problem is that you need to split out the conversion to be able to test for a bad input condition. Take a look at this code.

            Console.WriteLine("What is the radius of your circle: ");
        var isNumber = Double.TryParse(Console.ReadLine(), out double number);
        if (!isNumber)
            number = 0;
        Console.WriteLine("The area of your circle is: " + circleArea(number).ToString());
        Console.ReadKey();

This will test for a legitimate number and if it's not, it just passes zero as the number.