修复System.FormatException

Question

I am writing a code that will look at a group in a text file called a, and if a line in that code contains the phrase "Savings Found" it will write out that line, and if has 30% or more savings it will place an asterisk in front and if it contains 30% or more and has $500 or more savings, it will place two asterisks. Below I have a sample data, an example of what the console needs to look like, and the code I have thus far:

    string find = "Savings found:";
    foreach (var line in a.Where(w => w.Contains(find)))
       {
          var subStr = line.Substring(line.IndexOf(find) + find.Length);
          var startIndex = subStr.IndexOf('(');
          var endIndex = subStr.IndexOf(')');

          var savings = double.Parse(subStr.Substring(0, startIndex - 1).Trim());
          var percent = double.Parse(subStr.Substring(startIndex + 1, endIndex - startIndex - 2).Trim());

          Console.WriteLine("{0}{1}{2}", (percent >= 30) ? "*" : string.Empty,

          (percent >= 30 && savings >= 500) ? "*" : string.Empty,
                                                        line);
         }

Sample data/example

* 5/21/2015 11:55:56 PM | Batch 6|386/767|50.33 %|CH2M-R|Processed NXRMN5...Checking refundable and non-refundable fares. Traditional Booking. Inside ticketing window. Minimum Savings Required: $131.00. Actual Savings: $257.18. Savings found: $257.18 (11.55 %). Savings were previously found.

The problem that I am having is I am getting a FormatException error, and I think I know what the problem is. The problem is that the value of subString is the 257.18 and everything after that. I don't want everything after it I just want the number. What can I do to get rid of that extra junk so it can compile?

This problem is similar to a previous question asked, however in that answer I get an ArgumentIndexOutOfBounds exception, tried to fix it, but did not go far in actually fixing the problem, hence the reasoning behind this question.

Answer 1

You can use regex for that:

foreach(string line in a)
{
    Match m = Regex.Match(line, @"Savings\s+found:\s*\$(?<savings>\d+\.\d+)\s*\(\s*(?<percent>\d+\.\d+)\s*%");
    if (m.Success)
    {
        decimal savings = decimal.Parse(m.Groups["savings"].Value, CultureInfo.InvariantCulture);
        decimal percent = decimal.Parse(m.Groups["percent"].Value, CultureInfo.InvariantCulture);
        string prefix = string.Empty;
        if (percent >= 30)
        {
            if (savings >= 500)
                prefix = "**";
            else
                prefix = "*";
        }
        Console.WriteLine(prefix + line);
    }
}

Answer 2

It seems you are able to reproduce the error. That's great! Reproduceable problems are typically easy to fix.

Assuming you have no other tools like OzCode or ReSharper, this would be the way of debugging and fixing it:

Once you know the line in which the error occurs, make the statement simpler. That is, break it down into smaller parts. In your case

var savings = double.Parse(subStr.Substring(0, startIndex - 1).Trim());

Does too many things, so you don't really know what the problem is. Split that into:

var savingsString = subStr.Substring(0, startIndex - 1).Trim();
var savings = double.Parse(savingsString);

Because then, during debugging, you can add a watch to savingsString and see that it is

You can think about the fact why "$257.18" cannot be parsed and find counter measures to it. With the code before, you didn't even know the input which caused the problem.

Potential countermeasures:

• remove the dollar: .Replace("$","")
• start the substring later: subStr.Substring(1, ...)
• savingsString = savingsString.Trim('$'); if you cannot be sure whether it is in the beginning or the end

From your program code, it seems you know all required methods, you just don't know how to debug.

Continue with this approach and you'll be able to fix all problems of your code and even future problems.

And: I can't recommend Regex. They are unreadable and nobody wants to maintain them.

Answer 3

I'm assuming you want the number and decimal values after "Savings found:" regex should help. Theres probably a better way than this, but this should work.

 string find = "Savings found:";
    foreach (var line in a.Where(w => w.Contains(find)))
       {
          //line = 5/21/2015 11:55:56 PM | Batch 6|386/767|50.33 %|CH2M-R|Processed NXRMN5...Checking refundable and non-refundable fares. Traditional Booking. Inside ticketing window. Minimum Savings Required: $131.00. Actual Savings: $257.18. Savings found: $257.18 (11.55 %). Savings were previously found."
          Regex regex = new Regex(@"Savings found:\s\$[0-9]*.[0-9]{2}\s*\([0-9]*.[0-9]{2} %\)");
          Match match = regex.Match(line);
          var savingsFoundSection = match.Value;

          MatchCollection matches = Regex.Matches(savingsFoundSection, @"[0-9]*\.[0-9]{2}");
          String savingsString = matches[0].Value;
          String percentString = matches[1].Value;
          //savingString = "257.18"
          //precentString = "11.55"

          var savings = double.Parse(savingsString);
          var percent = double.Parse(percentString);

          Console.WriteLine("{0}{1}{2}", (percent >= 30) ? "*" : string.Empty,

          (percent >= 30 && savings >= 500) ? "*" : string.Empty,
                                                        line);
         }