If you mean storing program variables, I can explain that in detail, but I'm not familiar with terms like sto+ or sto-, so I'd appreciate if you could clarify that to me. For sum sigma, you'd iterate over the length of the array with a FOR loop, and increment a variable initialized at 0 for each iteration. E.g: SUM=0 FOR I=0 TO LEN(ARR)-1 INC SUM,ARR[I] NEXT PRINT "SUM IS ";SUM