Convert String to Integer

Question

Possible Duplicate:
how can I convert String to Int ?

Hi,

I have the following problem converting string to an integer:

string str = line.Substring(0,1);

//This picks an integer at offset 0 from string 'line'

So now string str contains a single integer in it. I am doing the following:

int i = Convert.ToInt32(str);

i should be printing an integer if I write the following statement right?

Console.WriteLine(i);

It compiles without any error but gives the following error on runtime:

An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll

Additional information: Input string was not in a correct format.

Any help please?

Answer 1

It's entirely possible there is some whitespace in there. Try running something akin to trim() (I'm not sure what language you're in) that will strip the white space. Also, try printing out the string to make sure you actually have the right part of it. We've all done that :)

Answer 2

FormatException

value does not consist of an optional sign followed by a sequence of digits (0 through 9).

The exception that is thrown when the format of an argument does not meet the parameter specifications of the invoked method.

You can use Int32.TryParse if you don't want to generate an exception like this.

Int32.TryParse: Converts the string representation of a number to its 32-bit signed integer equivalent. A return value indicates whether the operation succeeded.

Answer 3

Rather than using Convert.ToInt32(string) you should consider using Int32.TryParse(string, out int) instead. The TryParse methods are there to help deal with user-provided input in a safer manner. The most likely cause of your error is that the substring you are returning has an invalid string representation of an integer value.

string str = line.Substring(0,1);
int i = -1;
if (Int32.TryParse(str, out i))
{
   Console.WriteLine(i);
}

Answer 4

It's likely that your input is not a valid format. Try this instead. If the number is not valid, it should output an error.

Keep in mind that the string should consist of an optional sign followed by a number.

string line = "23"; // or whatever.
string str = line.Substring(0,1);
int i = 0;
if (Int32.TryParse(str, out i)) {
   Console.WriteLine(i);
} else {
    Console.WriteLine ("Error converting '" + line + "', '" + str + "'.");
}

One thing you may be seeing is the user entering "-1" for example. If you do the substring(0,1) on that, you'll only get "-" which isn't really valid.

Answer 5

Are you sure that the value returned in str is an int, set a debug point if your using visual studio. Ive got a feeling your problem maybe that your not actually returning an integer. Try:

line.Trim().Substring(0,1);

This will remove any whitespace.