Input string was not in a correct format (double)

Question

I'm trying to convert a string (ex. "0.20055") to its equivalent double.

I already know that for some reason that string does not contain a valid double, but I don't understand why.

I really need to be able to convert this string to a double... Could anyone explain me why it's not a valid double? And how to fix this?

Here is some of my code:

double[] values_in_double = null;
string[] values_in_string = lines[j].Split(',');
for(int x=0; x < numCols; x++)
{
    double val;
    bool r = double.TryParse(values_in_string[x],out val);
    if (!r)
        return;
    values_in_double[x] = Convert.ToDouble(values_in_string[x]);

}

As you can see I have a string[] of lines, in which a line is like:

0.20055,0.37951,0.39641,2.0472,32.351,0.38825,0.24976,1.3305,1.1389,0.50494

and I split them. But then I need to convert each one to a double value.

Answer 1

The main changes I would make to your code are to

1. remove the return statement since that will exit our method prematurely
2. use a List<double> to store your doubles (you don't have to declare a size ahead of time, which is nice because we don't know for sure how many items in the string will successfully convert to a double)
3. to use the val variable when adding it to the List, since double.TryParse has assigned the value to this variable already.

I also added a check to ensure that the variable numRows is not larger than the string array, because that would cause an exception in our loop:

// Mock values read from file
var input = new StringBuilder();
input.Append("0.20055,0.37951,0.39641,2.0472,32.351,0.38825,0.24976,1.3305‌​,");
input.Append("1.1389,0.50494,0.24‌​976,0.6598,0.1666,0.‌​24976,497.42,0.73378‌​,");
input.Append("2.6349,0.24976,0.14‌​942,43.37,1.2479,0.2‌​1402,0.11998,0.47706‌​,");
input.Append("‌​0.50494,0.60411,1.4‌​582,1.7615,5.9443,0.‌​11788,593.27,0.50‌​591,");
input.Append("0.12804,0.66295,0.14942,94.14,‌​3.8772,0.56393,0.214‌​02,1.741,");
input.Append("1.5‌​225,49.394,0.1853,0.‌​11085,2.042,0.051402,0.12804,114‌​.42,");
input.Append("71.05,1.0097,348690,0.12196,0.39‌​718,0.87804,0.37854,‌​0.25792,");
input.Append("2.2437,2.248‌​,0.001924‌​,8.416,5.1372,82.658‌​,4.4158,7.4277");

string[] values_in_string = inputString.ToString().Split(',');

// Declare values_in_double as a List so we don't have to worry about sizing
List<double> values_in_double = new List<double>();

// We will get errors if numCols is larger than our string array, so to be safe,
// set a variable that is the smallest of either numCols or our string array length
var numIterations = Math.Min(numCols, values_in_string.Length);

for (int x = 0; x < numIterations; x++)
{
    double val;

    // If TryParse succeeds, 'val' will contain the double value, so add it to our List
    if (double.TryParse(values_in_string[x], NumberStyles.Any, 
        System.Globalization.CultureInfo.InvariantCulture, out val))
    {
        values_in_double.Add(val);
    }
}

There is also a much shorter way to write this code. The line basically says: For each item in values_in_string, Where double.TryParse returns true, Select val (the item as a value) And convert all the val items into a List:

string[] values_in_string = inputString.ToString().Split(',');
double val = 0;

List<double> values_in_double = values_in_string
    .Where(value => double.TryParse(value, NumberStyles.Any, 
        System.Globalization.CultureInfo.InvariantCulture, out val))
    .Select(v => val)
    .ToList();