Csharp/C Sharp/Language Basics/Main

Deal with the arguments

 
using System;
class SayHello {
    public static void Main(string[] args) {
        if (args.Length > 0) {
            foreach (string arg in args) {
                if (arg.Equals("/help"))
                    Console.WriteLine("Run this program as follows: sayhello.exe [name1] ");
                else
                    Console.WriteLine("Hello " + "{0}", arg);
            }
        } else
            Console.WriteLine("For help, run sayhello.exe /help");
    }
}

Every console app starts with Main

/*
Learning C# 
by Jesse Liberty
Publisher: O"Reilly 
ISBN: 0596003765
*/
 namespace NotePad
 {
    public class HelloWorld
    {
       // every console app starts with Main
       static void Main()
       {
          System.Console.WriteLine("Hello world!");
       }
    }
 }

Main Function: Multiple Mains

// error 
using System;
class Complex
{
    static int Main()
    {
        // test code here
        Console.WriteLine("Console: Passed");
        return(0);
    }
}
public class TheMainFunctionMultipleMains
{
    public static void Main(string[] args)
    {
        foreach (string arg in args)
        Console.WriteLine(arg);
    }
}

Return different value to the operating system based on the argument length

 
using System;
class SayHello {
    public static int Main(string[] args) {
        if (args.Length > 0) {
            foreach (string arg in args) {
                if (arg.Equals("/help")) {
                    Console.WriteLine("Run this program as follows:" +
                              "sayhello.exe [name1] ");
                    return (1);
                } else
                    Console.WriteLine("Hello " + "{0}", arg);
            }
            return (0);
        } else
            Console.WriteLine("For help, run sayhello.exe /help");
        return (2);
    }
}

Static Main function

/*
Learning C# 
by Jesse Liberty
Publisher: O"Reilly 
ISBN: 0596003765
*/
 using System;
 namespace StaticTester
 {
     // create the class
    public class StaticTester
    {
       // Run is an instance method
       public void Run()
       {
           Console.WriteLine("Hello world");
       }
       // Main is static
       static void Main()
       {
           // create an instance
           StaticTester t = new StaticTester();
           // invoke the instance method
           t.Run();
       }
    }
 }

The Main Function

using System;
public class TheMainFunction
{
    public static void Main()
    {
        Console.WriteLine("Hello, Universe!");
    }
}

The Main Function:Command-Line Parameters

using System;
public class CommandLineParameters
{
    public static void Main(string[] args)
    {
        foreach (string arg in args)
        Console.WriteLine("Arg: {0}", arg);
    }
}

The Main Function:Returning an Int Status

using System;
public class ReturninganIntStatus
{
    public static int Main()
    {
        Console.WriteLine("Hello, Universe!");
        return(0);
    }
}

This is a simple C# program

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
/*  
   This is a simple C# program. 
 
   Call this program Example.cs. 
*/ 
 
using System; 
 
public class ExampleWriteLine { 
 
  // A C# program begins with a call to Main(). 
  public static void Main() { 
    Console.WriteLine("A simple C# program."); 
  } 
}

Using command-line arguments to initialize an array.

using System;
public class InitArray
{
   public static void Main( string[] args )
   {
         int arrayLength = Convert.ToInt32( args[ 0 ] );
         int[] array = new int[ arrayLength ]; // create array
         int initialValue = Convert.ToInt32( args[ 1 ] );
         int increment = Convert.ToInt32( args[ 2 ] );
         for ( int counter = 0; counter < array.Length; counter++ )
            array[ counter ] = initialValue + increment * counter;
         Console.WriteLine( "{0}{1,8}", "Index", "Value" );
         for ( int counter = 0; counter < array.Length; counter++ )
            Console.WriteLine( "{0,5}{1,8}", counter, array[ counter ] );
   }
}

Variations on the Main() Method

 
/*
The previous iteration of Main() was defined to take a single parameter (an array of strings) and return an integer data type. This is not the only possible form of Main(), however. It is permissible to construct your application¡�s entry point using any of the following signatures (assuming it is contained within a C# class or structure definition):
// No return type, array of strings as argument. 
public static void Main(string[] args) 
{ 
} 
// No return type, no arguments. 
public static void Main() 
{ 
} 
// Integer return type, no arguments. 
public static int Main() 
{ 
} 
*/