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Command-Line Arguments (C# Programming Guide)

The Main method can use arguments, in which case, it takes one of the following forms:

static int Main(string[] args)

static void Main(string[] args)
NoteNote:

To enable command-line arguments in the Main method in a Windows Forms application, you must manually modify the signature of Main in program.cs. The code generated by the Windows Forms designer creates a Main without an input parameter. You can also use Environment.CommandLine or Environment.GetCommandLineArgs to access the command-line arguments from any point in a console or Windows application.

The parameter of the Main method is a String array that represents the command-line arguments. Usually you determine whether arguments exist by testing the Length property, for example:

if (args.Length == 0)
{
    System.Console.WriteLine("Please enter a numeric argument.");
    return 1;
}

You can also convert the string arguments to numeric types by using the Convert class or the Parse method. For example, the following statement converts the string to a long number by using the Parse method:

long num = Int64.Parse(args[0]);

It is also possible to use the C# type long, which aliases Int64:

long num = long.Parse(args[0]);

You can also use the Convert class method ToInt64 to do the same thing:

long num = Convert.ToInt64(s);

For more information, see Parse and Convert.

The following example shows how to use command-line arguments in a console application. The program takes one argument at run time, converts the argument to an integer, and calculates the factorial of the number. If no arguments are supplied, the program issues a message that explains the correct usage of the program.

NoteNote:

When running an application in Visual Studio, you can specify command-line arguments in the Debug Page, Project Designer.

For more examples about how to use command-line arguments, see How to: Create and Use C# DLLs (C# Programming Guide).

public class Functions
{
    public static long Factorial(int n)
    {
        // Test for invalid input 
        if ((n < 0) || (n > 20))
        {
            return -1;
        }

        // Calculate the factorial iteratively rather than recursively: 
        long tempResult = 1;
        for (int i = 1; i <= n; i++)
        {
            tempResult *= i;
        }
        return tempResult;
    }
}

class MainClass
{
    static int Main(string[] args)
    {
        // Test if input arguments were supplied: 
        if (args.Length == 0)
        {
            System.Console.WriteLine("Please enter a numeric argument.");
            System.Console.WriteLine("Usage: Factorial <num>");
            return 1;
        }

        // Try to convert the input arguments to numbers. This will throw 
        // an exception if the argument is not a number. 
        // num = int.Parse(args[0]); 
        int num;
        bool test = int.TryParse(args[0], out num);
        if (test == false)
        {
            System.Console.WriteLine("Please enter a numeric argument.");
            System.Console.WriteLine("Usage: Factorial <num>");
            return 1;
        }

        // Calculate factorial. 
        long result = Functions.Factorial(num);

        // Print result. 
        if (result == -1)
            System.Console.WriteLine("Input must be >= 0 and <= 20.");
        else
            System.Console.WriteLine("The Factorial of {0} is {1}.", num, result);

        return 0;
    }
}
// If 3 is entered on command line, the 
// output reads: The factorial of 3 is 6.

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