Command-Line Arguments
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)
The parameter of the Main method is a string array that represents the command-line arguments. Usually you check for the existence of the arguments by testing the Length property, for example:
if (args.Length == 0)
{
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 on the Int64 class:
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 Method and Convert Class.
Example
In this example, the program takes one argument at run time, converts the argument to a long number, 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.
// Factorial_main.cs
// arguments: 3
using System;
public class Factorial
{
public static long Fac(long i)
{
return ((i <= 1) ? 1 : (i * Fac(i-1)));
}
}
class MainClass
{
public static int Main(string[] args)
{
// Test if input arguments were supplied:
if (args.Length == 0)
{
Console.WriteLine("Please enter a numeric argument.");
Console.WriteLine("Usage: Factorial <num>");
return 1;
}
// Convert the input arguments to numbers:
try
{
long num = long.Parse(args[0]);
Console.WriteLine("The Factorial of {0} is {1}.",
num, Factorial.Fac(num));
return 0;
}
catch (System.FormatException)
{
Console.WriteLine("Please enter a numeric argument.");
Console.WriteLine("Usage: Factorial <num>");
return 1;
}
}
}
Output
The Factorial of 3 is 6.
The following are two sample runs of the program assuming that the program name is Factorial.exe.
Run #1:
Enter the following command line: Factorial 10 You get the following result: The Factorial of 10 is 3628800.
Run #2:
Enter the following command line: Factorial You get the following result: Please enter a numeric argument. Usage: Factorial <num>
For more examples on using command-line arguments, see the example in Creating and Using C# DLLs.
See Also
Main | Return Values | General Structure of a C# Program | Command Line Parameters Tutorial
