C# 0 The Complete Reference

PART I

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PART IPART I

string

 array passed to 

Main( )

. The length of the 

args

 array will be equal to the number of 

command-line arguments, which might be zero.

For example, the following program displays all of the command-line arguments that it 

is called with:

// Display all command-line information.

using System;

class CLDemo {

  static void Main(string[] args) {

    Console.WriteLine("There are " + args.Length +

                       " command-line arguments.");

    Console.WriteLine("They are: ");

    for(int i=0; i < args.Length; i++)

      Console.WriteLine(args[i]);

  }

}

If

CLDemo

 is executed like this:

CLDemo one two three

you will see the following output:

There are 3 command-line arguments.

They are:

one

two

three

To understand the way that command-line arguments can be used, consider the next 

program. It uses a simple substitution cipher to encode or decode messages. The message 

to be encoded or decoded is specified on the command line. The cipher is very simple: To 

encode a word, each letter is incremented by 1. Thus, A becomes B, and so on. To decode, 

each letter is decremented. Of course, such a cipher is of no practical value, being trivially 

easy to break. But it does provide an enjoyable pastime for children.

// Encode or decode a message using a simple substitution cipher.

using System;

class Cipher {

  static int Main(string[] args) {

    // See if arguments are present.

    if(args.Length < 2) {

      Console.WriteLine("Usage: encode/decode word1 [word2...wordN]");

      return 1; // return failure code

    }

    // If args present, first arg must be encode or decode.

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    if(args[0] != "encode" & args[0] != "decode") {

      Console.WriteLine("First arg must be encode or decode.");

      return 1; // return failure code

    }

    // Encode or decode message.

    for(int n=1; n < args.Length; n++) {

      for(int i=0; i < args[n].Length; i++) {

        if(args[0] == "encode")

          Console.Write((char) (args[n][i] + 1) );

        else

          Console.Write((char) (args[n][i] - 1) );

      }

      Console.Write(" ");

    }

    Console.WriteLine();

    return 0;

  }

}

To use the program, specify either the “encode” or “decode” command followed by the 

phrase that you want to encrypt or decrypt. Assuming the program is called Cipher, here 

are two sample runs:

C:>Cipher encode one two

pof uxp

C:>Cipher decode pof uxp

one two

There are two interesting things in this program. First, notice how the program checks 

that a command-line argument is present before it continues executing. This is very important 

and can be generalized. When a program relies on there being one or more command-line 

arguments, it must always confirm that the proper arguments have been supplied. Failure to 

do this can lead to program malfunctions. Also, since the first command-line argument must 

be either “encode” or “decode,” the program also checks this before proceeding.

Second, notice how the program returns a termination code. If the required command 

line is not present, then 1 is returned, indicating abnormal termination. Otherwise, 0 is 

returned when the program ends.