The error invalid Pointer Operation on delphi 7 - delphi

Question

procedure searchAndReceipt;
var
amt, counter, check: integer;
gtinStore, qtyStore: array of integer;
totalCost: real;
begin
check := 0;
totalCost := 0.0;
write('Enter how many products you are purchasing: ');
repeat
readln(amt);
if (amt > 11) and (amt <= 0) then
writeln ('Please re-enter how many products are you purchasing with a value between 1-10')
else
check:= 1;
until check = 1;
SetLength(gtinStore, amt);
SetLength(qtyStore, amt);
SetLength(receiptArray, amt);
for counter:=1 to amt do
begin
write('Enter a GTIN code: ');
repeat
readln(gtinStore[counter]);
if (gtinStore[counter] >= 99999999) and (gtinStore[counter] <= 1000000) then
writeln ('Please re-enter the Gtin Code with a value of 8 digits')
else
check:= 1;
until check = 1;
check := 0;
write('Enter the Quantity: ');
repeat
readln(qtyStore[counter]);
if (qtyStore[counter] >= 11) and (qtyStore[counter] <= 0) then
writeln ('Please re-enter the quantity with a value between 1-10')
else
check:= 1;
until check = 1;
end;
assign(stockFile,'stockFile.dat');
Reset(stockFile);
counter:=1;
while not EOF(stockFile) do
begin
receiptArray[counter].productName := ('Product Not Found');
receiptArray[counter].productGTIN := 0;
receiptArray[counter].productPrice := 0.0;
inc(counter);
end;
read (stockFile, Stock);
for counter:=1 to amt+1 do
begin
while not EOF(stockFile) do
begin
read (stockFile, Stock);
if Stock.productGTIN = gtinStore[counter] then
receiptArray[counter].productGTIN:= Stock.productGTIN;
receiptArray[counter].productName:= Stock.productName;
receiptArray[counter].productPrice:= Stock.productPrice;
end;
end;
assign(receiptFile, 'receipt.txt');
rewrite(receiptFile);
for counter:= 1 to amt+1 do
begin
if receiptArray[counter].productName = 'Product Not Found' then
begin
writeln(receiptFile, 'GTIN: ', gtinStore[counter]);
writeln(receiptFile, receiptArray[counter].productName);
writeln(receiptFile, '');
end
else
begin
writeln(receiptFile, 'GTIN: ',gtinStore[counter]);
writeln(receiptFile, 'Name: ',receiptArray[counter].productName);
writeln(receiptFile, 'Quantity: ', qtyStore[counter]);
writeln(receiptFile, 'Price: £',receiptArray[counter].productPrice*qtyStore[counter]:4:2);
writeln(receiptFile, '');
totalCost := ((receiptArray[counter].productPrice * qtyStore[counter]) + totalCost);
end;
end;
choices:=1;
end;
begin
choices:= 1;
while choices <> 3 do
begin;
writeln('Press 1 to create the stock file');
writeln('Press 2 to search for an item and print a receipt');
writeln('Press 3 to exit');
write('Choice: ');
readln(choices);
writeln;
case choices of
1: createStock;
2: searchAndReceipt;
end;
end;
end.
I run this procedure (there's another procedure before this that places stock into a file), what this is supposed to do is to take that stock out and place it into a text file... however after I've entered the GTIN number and the quantities of the items my program produces this error
Exception EAccessViolation in module Task_2.exe at 00002550.
Access violation at address 00402550 in module 'Task_2.exe'. Read of address 03491DD4.
within the shell, and a message box pops up saying
Project Task_2.exe raised exception class EInvalidPointer with message 'invalid Pointer Operation'. Process Stopped
Thanks in advance

Answer 1

Dynamic arrays are 0-based, but your code assumes 1-based indexing. Hence you index off the end of the array, and hence the runtime errors. Fix the code by using 0-based indices. That is loop from 0 to N-1 rather than from 1 to N.
Even what you fix that, you have loops that run from 1 to N+1 so you aren't even allocating enough space for your arrays.
You should enable range checking in the compiler options so that the compiler can emit diagnostics code to give you better error messages.