Invalid pointer operation; Recursive Merge Sort - delphi

Question

I've attempted to implement a merge sort for strings however I cannot perform the recursive part and I get the error "Invalid Pointer Operation"
program Project1;
{$APPTYPE CONSOLE}
uses
SysUtils;
var i : Integer;
const MyArray : array[1..5]of string = ('hi', 'zebra', 'apple', 'Xylophone', 'dog');
Procedure merge(result, left, right : array of string);
var i, i1, i2 : Integer;
begin
i1 := 0;
i2 := 0;
for i := 0 to Length(result) do
begin
if (i2 >= Length(right)) or (i1 < Length(left)) and (StrComp(PChar(left[i]), PChar(right[i2])) < 0) then
begin
result[i] := left[i1];
inc(i1);
end
else
begin
result[i] := right[i2];
inc(i2);
end;
end;
end;
Procedure mergeSort(OriginalList : array of string);
var left, right : array of string;
i : Integer;
begin
if (Length(OriginalList) >= 2) then
begin
setlength(left, length(OriginalList) div 2);
setlength(right, length(OriginalList) - (length(OriginalList) div 2));
for i := 0 to Length(left) do
begin
left[i] := OriginalList[i];
end;
for i := 0 to Length(right) do
begin
right[i] := OriginalList[i + Length(OriginalList) div 2];
end;
mergeSort(left);
mergeSort(right);
merge(OriginalList, left, right);
end;
end;
begin
writeln('The data before sorting: ');
for i := low(MyArray) to High(MyArray) do
begin
write(MyArray[i]+' ');
end;
writeln;
mergeSort(MyArray);
writeln('The data before sorting: ');
for i := low(MyArray) to High(MyArray) do
begin
write(MyArray[i]+' ');
end;
readln;
end.
On the line in the mereSort function where I recall the merge sort function on the arrays "left" and "right", I get the error message but I don't quite understand why?

Answer 1

There are many different things wrong with this, hopefully these points will help you in the right direction.
Problems with Array Indexes
You are indexing beyond the end of your arrays:
Dynamic arrays are indexed starting from zero so the line
for i := 0 to Length(left) do
should be
for i := 0 to Length(left) - 1 do
or you can use
for i := Low(left) to High(left) do
As you did later.
I would recommend you choose a standard form and use it consistently, and also that you avoid declaring constant arrays with non-zero based indexing unless you have good reason, this way you can use the same forms consistently or change the type of array later without running into trouble
This first fix will stop your program crashing, but you'll notice your sort code isn't changing anything...
Problems with parameter passing
Delphi has several different ways to pass parameters into procedures:
procedure doSomething(a : array of string);
procedure doSomething(var a : array of string);
procedure doSomething(out a : array of string);
procedure doSomething(const a : array of string);
These determine how what happens inside the procedure can affect the original variable passed
This is something you will need to understand, read up in the documentation:
http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Parameters_(Delphi)
There is IMO some very confusing behaviour and syntax relating to array parameters and a lot of stuff that seems intuitive is not allowed especially with XE/older version, its worth reading the documentation about the standard data types
In the current state, your merge procedure will have no effect because it only operates on a new copy of the array you pass in, which you have also declared as constant
Other
I would avoid the use of result as a procedure parameter since this is the name used for function return values, it seems like asking for trouble to use it like that.
PS: I haven't looked at the logic of the merging, just the basic language mistakes