How to find the starting and the ending element positions of an array

[bholas]

If you're often having to change array sizes and/or starting indexes, you may also have to make changes in multiple locations inside the program. Let's take a look at following arrays for example:
var
a1 : array [ 0 .. 5] of integer;
a2 : array [10 .. 60] of integer;
Listing #1 : Delphi code. Download arrays (0.18 KB).


One way to go through all array items is to hard code the starting and ending indexes of the array:
for i := 10 to 60 do
begin
//
// your code goes here...
// a2[ i ]
//
end;
Listing #2 : Delphi code. Download arrays2 (0.21 KB).


On the other hand, you can use "Low()" and "High()" functions to find the starting and the ending element positions of an array.
//
// following function call
// will return 10 (starting index)
// because a2 was defined as:
// a2 : array [10 .. 60] of integer;
//
Low( a2 )

//
// following function call
// will return 5 (ending index)
// because a1 was defined as:
// a1 : array [ 0 .. 5] of integer;
//
High( a1 )
Listing #3 : Delphi code. Download arrays3 (0.29 KB).


This could come in handy when you have to iterate through a list of items in an array without hard coding the size of the array. For example:
for i := Low( a2 ) to High( a2 ) do
begin
//
// your code goes here...
// a2[ i ]
//
end;
Listing #4 : Delphi code. Download arrays4 (0.22 KB).

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