Answer to Chrissie's puzzle
0 1 2 3 4 5 6 7 8 9
C K Z E N S A O I D
K and C can easily be identified as 1 and 0 respectively. In the left-most column A can only be added to 0 or 10 to give A, but C was identified as 0 therefore D=9 and a carry over was gained from the previous column.
Using similar logic the other letters can be identified (remembering that N is smaller than 7).