.NET Tip: Converting Strings to Numbers
First, take a look at the Convert class. The Convert class offers methods to convert to and from every base data type, but for the purpose of this tip I'm only going to use the Convert.ToInt32() method. The method accepts a string parameter and returns an integer. If you pass in a string containing a valid integer value, the method returns an integer as expected. If you pass in a null value, the value 0 is returned. If you pass in a string that cannot be converted to an integer, an exception is raised. Here are examples of calls to the Convert.ToInt32() method with the comment indicating the result.
int x; x = Convert.ToInt32("123"); // x = 123 x = Convert.ToInt32(null); // x = 0 x = Convert.ToInt32("abc"); // System.FormatException
Another option is to use the Parse() method available on the numeric base data types. For my purpose, I'm going to stick with int.Parse() for my examples. As with Convert.ToInt32(), if you pass in a string containing a valid integer value, the method returns an integer as expected. Passing in null or a string that cannot be converted, however, results in System.ArgumentNullException and System.FormatException exceptions respectively. Here is how you would use int.Parse().
int x; x = int.Parse("123"); // x = 123 x = int.Parse(null); // System.ArgumentNullException x = int.Parse("abc"); // System.FormatException
int x; bool b; b = int.TryParse("123", out x); // x = 123, b = true b = int.TryParse(null, out x); // x = 0, b = false b = int.TryParse("abc", out x); // x = 0, b = false
Depending upon your application, one of these methods of converting strings to numbers may have an advantage over the others. I just want to make you aware of how the different options behave so you are able to make good decisions when designing your application.
About the Author
Jay Miller is a Software Engineer with Electronic Tracking Systems, a company dedicated to robbery prevention, apprehension, and recovery based in Carrollton, Texas. Jay has been working with .NET since the release of the first beta and is co-author of Learn Microsoft Visual Basic.Net In a Weekend. Jay can be reached via email at firstname.lastname@example.org.