C# How can I handle this exception?

Question

I am new to C# and trying to create a GPA calculator using a sentinel controlled loop. To end the loop, I want the user to enter an 'x', but it is throwing an exception. I'm pretty sure it is because 'x' is not a double type, but I am not sure how I can make it work. I was using a number to exit before but it kept being added to the gradeTotal. Any suggestions would be great! Thanks!

Code:

class Program
{
    static void Main(string[] args)
    {


        double gradeTotal = 0;
        int[] score = new int[100];
        string inValue;
        int scoreCnt = 0;
        Console.WriteLine("When entering grades, use a 0-4 scale. Remember; 
        A = 4, B = 3, C = 2, D = 1, F = 0");
        Console.WriteLine("Enter grade {0}: ((X to exit)) ", scoreCnt + 1);
        inValue = Console.ReadLine();
        gradeTotal += double.Parse(inValue);//This may be a problem area
        while (inValue != "x")
        {
            if (int.TryParse(inValue, out score[scoreCnt]) == false)
                Console.WriteLine("Invalid data -" + "0 stored in array");
            ++scoreCnt;
            Console.WriteLine("Enter Score{0}: ((X to exit)) ", scoreCnt + 
            1);
            inValue = Console.ReadLine();
            gradeTotal += double.Parse(inValue);//This is a problem area
        }
        Console.WriteLine("The number of scores: " + scoreCnt);
        Console.WriteLine("Your GPA is: " + gradeTotal);//Obviously not the 
        //right calculation, just trying to figure it out
        Console.ReadLine();
    }
}

That will happen if any non-numeric key is pressed. Use [Int.TryParse()](https://stackoverflow.com/questions/4804968/how-can-i-validate-console-input-as-integers) instead, that will tell you if its a valid integer. (no need for a double as you are only looking for 0 to 4) — Alex K., Aug 15 '17 at 18:18
Please pick duplicate of your choice from results of the search - https://www.bing.com/search?q=c%23+formatexception+double — Alexei Levenkov, Aug 15 '17 at 18:21
Even when I use int.TryParse() I get "An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll Additional information: Input string was not in a correct format." — sandracodes, Aug 15 '17 at 18:24
Possible duplicate of [C# testing to see if a string is an integer?](https://stackoverflow.com/questions/1752499/c-sharp-testing-to-see-if-a-string-is-an-integer) — Loren_, Aug 15 '17 at 19:23

score 0 · Accepted Answer · answered Aug 15 '17 at 18:21

Least effort

Instead of

gradeTotal += double.Parse(inValue);//This is a problem area

Try

if (inValue == "X") break;
gradeTotal += double.Parse(inValue);

More robust

double d;
var ok = double.TryParse(inValue, out d);
if (!ok) break;
gradeTotal += d;

score 0 · Answer 2 · answered Aug 15 '17 at 18:21

You have zero validation on the inValue before trying to parse it. That's the problem. How you resolve this is up to you. Here's a couple suggestions:

wrap the code in a try...catch...

try {

 grandTotal += double.Parse(inValue);

} catch (Exception e) {

 Console.WriteLine("Invalid input!");

}

Use Regular Expressions to validate user input and return error if not a number (System.Text.RegularExpressions.Regex)

C# How can I handle this exception?

2 Answers2