Structure of a Delphi Console Application
In our previous lesson Setting up and compiling a Delphi Console Application, we wrote this very
basic example:
program ConsoleTest;
{$APPTYPE CONSOLE}
uses SysUtils;
begin
WriteLn('Program ConsoleTest is running.');
WriteLn('Press the ENTER key to stop');
ReadLn;
end.
Let's have a look at the meaning of the different keywords in the source code:
- program means that this unit as the program's main source unit, the .DPR file.
This keyword is followed by the name of the project file, without the extension .DPR.
When you compile
a project, Delphi uses the name of the project file for the name of your EXE file that it creates.
- $APPTYPE controls whether to generate a console application or a graphical
UI application (UI = User Interface). Here, the {$APPTYPE CONSOLE} directive tells
the compiler to generate
a console application.
- uses is followed by a list of all the units that the unit ConsoleTest
uses, that is: the other units that are part of the project.
We see that Delphi included the SysUtils unit. Also another unit
is included, the
System unit, but since System is included in every Delphi program, it's not necessary to mention it in the uses directive.
- In between the keywords begin and end you add your code.
Note that the last end keyword is always followed by a dot character -- also called point,
period, or final stop. As you've probably guessed ;) this indicates the end of the project
file.
Handling Input and Output
In a console application, you don't use VCL controls for input and output. Communication with the
user is handled with Read and Write commands:
- WriteLn displays a message, followed by an end-of-line code that
positions the text cursor at the beginning of the next line.
Example: display the line of text Program ConsoleTest is running :
WriteLn('Program ConsoleTest is running');
- ReadLn inputs keystrokes, until the ENTER ("return") key is pressed.
Example: read data until Enter is pressed and put in variable S:
ReadLn(S);
Example: simply wait until Enter is pressed:
ReadLn;
- Write displays data without an end-of-line.Thus, the ouput of the next Write command
will appear directly after the displayed text.
Example: display 3 strings on the same line:
Write('one '); // note the space after the word
Write('two '); // note the space after the word
Write('three');
- Read to directly input data to one or more variables. The Read command waits until the
number of data values that are typed (separated by spaces, if more than 1 value) is equal to the number
of variables provided.
Sounds complicated, doesn't it? That's why Read isn't used often,
most input is done with ReadLn.
Example to input a single character to variable C, given that C is of
type "char" (press ENTER afterwards) :
Read(C);
To be continued...
« Part 1: Setting up and Compiling a Console Application
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