array of checkbox values

Hallo, I have a form with a number of checkboxes grouped together. The value of these boxes is stored in an array: $used[]. Now I found that the value of checked boxes (value = 'Y') are stored in the array while non checked boxes are not stored at all. This makes the array incomplete as I want to have all checkbox values in the array. For example: for 4 checkboxes the values are checkbox 1: array index = 0 value = "Y" checkbox 2: array index = 1 value = "Y" checkbox 3: value = "N" : it does not occur in the array checkbox 4: array index = 2 value = "Y" Is there a way to, as it were, complete the array and have all values stored, even the "N" values? So that array index 2 has a value of "N", and array index 3 is "Y". Thxs Sjef