Recipe 1.2. Creating a Console Application

Problem

You want to develop a Console application that converts between the Fahrenheit, Celsius, and kelvin temperature systems.

Solution

Sample code folder: Chapter 01\ Console Version

Create a Windows Console application, and add logic to perform all the calculations based on the user's input. First, read through Recipe 1.1 for background information on using Visual Studio and on converting between the various temperature systems.

Discussion

Start Visual Studio 2005, and then use the File New Project menu command to create a new project. Select the Windows project type, and then select the Console Application template. Click OK to create the new project. Since a console application doesnt have a special user interface, Visual Studio simply displays the default code block for the new project:

   Module Module1    Sub Main( )    End Sub End Module 

There are a few different ways to rename the module. If you only want to change the name in the code, just replace the word "Module1" with something like "Convert-Temperature":

 Module ConvertTemperature 

Unfortunately, this requires you to make a change to the project's properties. Before the change, Visual Studio planned to start the program from the Sub Main routine in the Module1 module. But since you changed the name, there is no longer a Module1 for Visual Studio to use.

To modify the properties, select the Project ConsoleApplication1 Properties menu command, or double-click on the My Project item in the Solution Explorer panel. When the Project Properties window appears, the Application tab in that window should already be active. To change the starting code for the program, select "ConvertTemperature from the "Startup object" field. Then close the Project Properties window, and return to the code.

If you want to avoid all of this unpleasantness, rename the module's filename instead of its name in the code. To do this, right-click the Module1.vb file in the Solution Explorer, choose the Rename command from the shortcut menu that appears, and give it a new name such as ConvertTemperature.vb. (Don't forget the .vb extension.) Visual Studio will change the module name as well and fix up all the other loose connections.

All of the conversion code will go in the Sub Main routine:

 Module ConvertTemperature    Sub Main( )       ' ----- The program starts here.       Dim userInput As String       Dim sourceType As String       On Error Resume Next       ' ----- Display general instructions.         Console.WriteLine("Instructions:" & vbCrLf & _          "To convert temperature, enter a starting " & _          "temperature, followed" & vbCrLf & _          "by one of the following letters:" & vbCrLf & _          "  F = Fahrenheit" & vbCrLf & _          "  C = Celsius" & vbCrLf & _          "  K = kelvin" & vbCrLf & _          "Enter a blank line to exit." & vbCrLf)       ' ----- The program continues until the user       ' enters a blank line.       Do While True          ' ----- Prompt the user.            Console.WriteLine("Enter a source temperature.")          Console.Write("> ")          userInput = Console.ReadLine( )          ' ----- A blank line exits the application.          If (Trim(userInput) = "") Then Exit Do          ' ----- Determine the source type.          userInput = UCase(userInput)          If (InStr(userInput, "F") > 0) Then             ' ----- Start with Fahrenheit.             sourceType = "F"             userInput = Replace(userInput, "F", "")          ElseIf (InStr(userInput, "C") > 0) Then             ' ----- Start with Celsius.             sourceType = "C"             userInput = Replace(userInput, "C", "")          ElseIf (InStr(userInput, "K") > 0) Then             ' ----- Start with kelvin.             sourceType = "K"             userInput = Replace(userInput, "K", "")          Else             ' ----- Invalid entry.             Console.WriteLine("Invalid input: " & _                userInput & vbCrLf)             Continue Do          End If          ' ----- Check for a valid temperature.          userInput = Trim(userInput)          If (IsNumeric(userInput) = False) Then               Console.WriteLine("Invalid number: " & _                userInput & vbCrLf)             Continue Do          End If          ' ----- Time to convert.          If (sourceType = "F") Then             ' ----- Convert from Fahrenheit to other types.               Console.WriteLine(" Fahrenheit: " & userInput)             Console.WriteLine(" Celsius: " & _                (Val(userInput) - 32) / 1.8)             Console.WriteLine(" kelvin: " & _                ((Val(userInput) - 32) / 1.8) + 273.15)          ElseIf (sourceType = "C") Then             ' ----- Convert from Celsius to other types.             Console.WriteLine(" Fahrenheit: " & _                (Val(userInput) * 1.8) + 32)             Console.WriteLine(" Celsius: " & userInput)             Console.WriteLine(" kelvin: " & _                Val(userInput) + 273.15)          Else             ' ----- Convert from kelvin to other types.             Console.WriteLine(" Fahrenheit: " & _                ((Val(userInput) - 273.15) * 1.8) + 32)             Console.WriteLine(" Celsius: " & _                Val(userInput) - 273.15)             Console.WriteLine(" kelvin: " & userInput)          End If       Loop       End    End Sub End Module 

Running the program opens up a command window. You will immediately be prompted to enter a source temperature. The program continues to convert values until it detects a blank line for input. Here is a typical short session:

 Instructions: To convert temperature, enter a starting temperature, followed by one of the following letters:   F = Fahrenheit   C = Celsius   K = kelvin Enter a blank line to exit. Enter a source temperature. > 37c   Fahrenheit: 98.6   Celsius: 37   kelvin: 310.15 Enter a source temperature. > 

Console applications bring back memories of those pre-Windows days when the 80-by-24-character console display was the primary user interface mechanism on the IBM PC platform. Text input and output, and maybe some simple character-based graphics and color, were all the visual glitz that a programmer could use.

Console applications in .NET use that same basic text-presentation system as their primary interface, but they also include the full power of the .NET libraries. For the actual user interaction, the Console object takes center stage. It includes features that let you display text on the console (Write(), WriteLine()), retrieve user input (Read(), ReadKey(), ReadLine()), and manipulate the console window in other useful ways.

The temperature conversion program uses the Console object and some basic temperature formulas within its core processing loop. First, it gets a line of input from the user and stores it as a string:

 userInput = Console.ReadLine( ) 

The input must be a valid number, plus the letter F, C, or K. The letter can appear anywhere in the number: 37C is the same as C37 is the same as 3C7. Once the program has extracted the numeric temperature and its source system, it performs the conversion; it then outputs the results using the Console.WriteLine() method.

See Also

The recipes in this chapter should be read together to gain a full understanding of general .NET application development concepts.