Indexing of Array

I am facing problem with indexing of array. In shopping cart i had used the array to store the product and for displaying, now here till certain limit it was working very fine, but when the index(key) of array in which items values where stores increased greater than 9 then it is creating problem it start changing values from the index from top of that array . it stores only 10 values 0-9, i had not defined restrictions to this array for transaction between the pages i had used cookies it is cookie problem or array ??? if any one is having any soln pls reply me ..... From Mitesh