When you're using ASP arrays, sometimes you want to make them larger part way through processing. The Redim command lets you alter an array size - and the preserve command saves the data already there.
Let's say you start out with an array that normally only needs around 5 items in it. So you could do
Dim ShopCart(5)
This would conserve memory space and take into account what most people would use it for. But let's say someone comes along who wants more than 5 items in their shopping cart! You don't want to lose that extra information. So to make the array size larger, you would say
Redim ShopCart(10)
or whatever new size you wanted to bump it up to. One problem, though. A redim command loses any data currently in the array. This might be fine if you're just getting started, but if someone is halfway through shopping it'd be bad to lose their data. In that case, you would instead use -
Redim PRESERVE ShopCart(10)
This keeps the array we had already and just adds more space to it.
