Arraylist index in C#

Question

I have an ArrayList and I want to give index as big integer value (Customer ID)

ex:

limitAmountTotal[CUSTOMERID] = amount;

where CUSTOMERID = 1000000

But I am getting an error

arraylist is out of range

Is there any way I can handle this in C#?

in PHP we can do this like this

$limitAmountTotal[$CUSTOMERID] = $amount;

Thanks

Answer 1

That's because ArrayList behaves like an array. You want Dictionary instead:

Dictionary<int, int> limitAmountTotal  = new Dictionary<int, int>();
limitAmountTotal[10000] = 30;

Answer 2

Use List<T> or simple Array (array is optional but not recommended for this!).

If your amount is some monetary value then you can try using:

decimal[] arr = new decimal[arraySize];

or:

List<decimal> list = new List<decimal>();

If not change decimal to whatever data type you like: int, long and etc.

Edit:

Some performance and memory tests:

All collections are type of `int`
Maximum collection size: 1000000
Random generated index used for value lookup: 354497

Array populating time elapsed: 00:00:00.0063499
Array lookup time elapsed: 00:00:00.0000004
Size: 4000028 bytes
==============
List populating time elapsed: 00:00:00.0184629
List lookup time elapsed: 00:00:00.0000004
Size: 4194509 bytes
==============
Dictionary populating time elapsed: 00:00:00.0593676
Dictionary lookup time elapsed: 00:00:00.0000293
Size: 17001335 bytes

Code: https://gist.github.com/rekosko/999e58dc95ba3e4fc678