1. Computing

How to Declare and Initialize Constant Arrays in Delphi

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In Delphi, arrays allow a developer to refer to a series of variables by the same name and to use a number (an index) to tell them apart.

In most scenarios, you declare an array as a variable - thus allowing for array elements to be changed at run-time.

Sometimes, you need to declare a constant array - a read-only array. You cannot change the value of a constant or a read-only variable. Therefore, while declaring a constant array you have to initialize it.

Here are a few examples of declaring and initializing constant arrays in Delphi:

 type
    TShopItem = record
      Name : string;
      Price : currency;
    end;
 
 const
    Days : array[0..6] of string =
    (
      'Sun', 'Mon', 'Tue', 'Wed',
      'Thu', 'Fri', 'Sat'
    ) ;
 
    CursorMode : array[boolean] of TCursor =
    (
      crHourGlass, crSQLWait
    ) ;
 
    Items : array[1..3] of TShopItem =
    (
      (Name : 'Clock'; Price : 20.99),
      (Name : 'Pencil'; Price : 15.75),
      (Name : 'Board'; Price : 42.96)
    ) ; 
The above code declares and initializes three constant arrays, named: "Days", "CursorMode" and "Items".

"Days" is a string array of 6 elements. Days[1] returns the "Mon" string.

"CursorMode" is an array of two elements, where by declaration CursorMode[false] = crHourGlass and CursorMode = crSQLWait. "cr*" constants can be used to change the current screen cursor.

 var
    isDatabaseOperation : boolean
 
 begin
    isDatabaseOperation := true;
 
    //changes the cursor to crSQLWait
    Screen.Cursor := CursorMode[isDatabaseOperation];
 

"Items" defines an array of 3 TShopItem records.

Note: trying to assign a value for an item in a constant array raises the "Left side cannot be assigned to" compile time error, as in:

 Items[1].Name := 'Watch'; //will NOT compile 

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