How to: Convert a String to a Number (C# Programming Guide)

You can convert a string to a number by calling the Parse or TryParse method found on the various numeric types (int, long, double, etc.), or by using methods in the System.Convert class.

If you have a string, it is slightly more efficient and straightforward to call a TryParse method (for example, int.TryParse("11", out number)) or Parse method (for example, var number = int.Parse("11")). Using a Convert method is more useful for general objects that implement IConvertible.

You can use Parse or TryParse methods on the numeric type you expect the string contains, such as the System.Int32 type. The Convert.ToInt32 method uses Parse internally. The Parse method returns the converted number; the TryParse method returns a Boolean value that indicates whether the conversion succeeded, and returns the converted number in an out parameter. If the string is not in a valid format, Parse throws an exception, whereas TryParse returns false. When calling a Parse method, you should always use exception handling to catch a FormatException in the event that the parse operation fails.

Calling the Parse and TryParse methods

The Parse and TryParse methods ignore white space at the beginning and at the end of the string, but all other characters must be characters that form the appropriate numeric type (int, long, ulong, float, decimal, etc.). Any white space within the string that forms the number causes an error. For example, you can use decimal.TryParse to parse "10", "10.3", or " 10 ", but you cannot use this method to parse 10 from "10X", "1 0" (note the embedded space), "10 .3" (note the embedded space), "10e1" (float.TryParse works here), and so on. In addition, a string whose value is null or String.Empty fails to parse successfully. You can check for a null or empty string before attempting to parse it by calling the String.IsNullOrEmpty method.

The following example demonstrates both successful and unsuccessful calls to Parse and TryParse.

using System;

public class StringConversion
{
    public static void Main()
    {
       string input = String.Empty;
       try
       {
           int result = Int32.Parse(input);
           Console.WriteLine(result);
       }
       catch (FormatException)
       {
           Console.WriteLine($"Unable to parse '{input}'");
       }
       // Output: Unable to parse ''

       try
       {
            int numVal = Int32.Parse("-105");
            Console.WriteLine(numVal);
       }
       catch (FormatException e)
       {
           Console.WriteLine(e.Message);
       }
       // Output: -105

        if (Int32.TryParse("-105", out int j))
            Console.WriteLine(j);
        else
            Console.WriteLine("String could not be parsed.");
        // Output: -105

        try
        {
            int m = Int32.Parse("abc");
        }
        catch (FormatException e)
        {
            Console.WriteLine(e.Message);
        }
        // Output: Input string was not in a correct format.

        string inputString = "abc";
        if (Int32.TryParse(inputString, out int numValue))
            Console.WriteLine(inputString);
        else
            Console.WriteLine($"Int32.TryParse could not parse '{inputString}' to an int.");
        // Output: Int32.TryParse could not parse 'abc' to an int.
     }
}

The following example illustrates one a approach to parsing a string that is expected to include leading numeric characters (including hexadecimal characters) and trailing non-numeric characters. It assigns valid characters from the beginning of a string to a new string before calling the TryParse method. Because the strings to be parsed contain a small number of characters, the example calls the String.Concat method to assign valid characters to a new string. For a larger string, the StringBuilder class can be used instead.

using System;

public class StringConversion
{
    public static void Main()
    {
        var str = "  10FFxxx";
        string numericString = String.Empty;
        foreach (var c in str) 
        {
            // Check for numeric characters (hex in this case) or leading or trailing spaces.
            if ((c >= '0' && c <= '9') || (Char.ToUpperInvariant(c) >= 'A' && Char.ToUpperInvariant(c) <= 'F') || c == ' ') {
                numericString = String.Concat(numericString, c.ToString());
            }
            else
            {
                break;
            }
        }
        if (int.TryParse(numericString, System.Globalization.NumberStyles.HexNumber, null, out int i))
            Console.WriteLine($"'{str}' --> '{numericString}' --> {i}");
            // Output: '  10FFxxx' --> '  10FF' --> 4351

        str = "   -10FFXXX";
        numericString = "";
        foreach (char c in str) {
            // Check for numeric characters (0-9), a negative sign, or leading or trailing spaces.
            if ((c >= '0' && c <= '9') || c == ' ' || c == '-') 
            {
                numericString = String.Concat(numericString, c);
            } else
                break;
        }
        if (int.TryParse(numericString, out int j))
            Console.WriteLine($"'{str}' --> '{numericString}' --> {j}");
            // Output: '   -10FFXXX' --> '   -10' --> -10
    }
}

Calling the Convert methods

The following table lists some of the methods from the Convert class that you can use to convert a string to a number.

Numeric Type Method
decimal ToDecimal(String)
float ToSingle(String)
double ToDouble(String)
short ToInt16(String)
int ToInt32(String)
long ToInt64(String)
ushort ToUInt16(String)
uint ToUInt32(String)
ulong ToUInt64(String)

The following example calls the Convert.ToInt32(String) method to convert an input string to an int. The example catches the two most common exceptions that can be thrown by this method, FormatException and OverflowException. If the resulting number can be incremented without exceeding Int32.MaxValue, the example adds 1 to the result and displays the output.

using System;

public class ConvertStringExample1
{
    static void Main(string[] args)
    {
        int numVal = -1;
        bool repeat = true;

        while (repeat)
        {
            Console.Write("Enter a number between −2,147,483,648 and +2,147,483,647 (inclusive): ");

            string input = Console.ReadLine();

            // ToInt32 can throw FormatException or OverflowException.
            try
            {
                numVal = Convert.ToInt32(input);
                if (numVal < Int32.MaxValue)
                {
                    Console.WriteLine("The new value is {0}", ++numVal);
                }
                else
                {
                    Console.WriteLine("numVal cannot be incremented beyond its current value");
                }
           }
            catch (FormatException)
            {
                Console.WriteLine("Input string is not a sequence of digits.");
            }
            catch (OverflowException)
            {
                Console.WriteLine("The number cannot fit in an Int32.");
            }

            Console.Write("Go again? Y/N: ");
            string go = Console.ReadLine();
            if (go.ToUpper() != "Y")
            {
                repeat = false;
            }
        }
    }
}
// Sample Output:
//   Enter a number between -2,147,483,648 and +2,147,483,647 (inclusive): 473
//   The new value is 474
//   Go again? Y/N: y
//   Enter a number between -2,147,483,648 and +2,147,483,647 (inclusive): 2147483647
//   numVal cannot be incremented beyond its current value
//   Go again? Y/N: y
//   Enter a number between -2,147,483,648 and +2,147,483,647 (inclusive): -1000
//   The new value is -999
//   Go again? Y/N: n

See also