Summing Values in an Array

coryco2

What would be the most compact, efficient SPIN code to use for summing the values in a variable array whose values change frequently?

I would like something better than Sum := ArrayItem[0] + ArrayItem[1] +...ArrayItem[n].

Any suggestions?

Duane Degn

One way is:

sum := 0
  repeat index from 0 to MAX_INDEX
     sum += arrayItem[index]

Electrodude

How often is the sum needed relative to how often values change?

If you need the sum only rarely, do what Duane Degn said. But if you need the sum every time you change any single value, update the sum every time you change a value by subtracting out the old value of the element you're about to overwrite and then adding in the new value, with something like this:

VAR

  long  sum
  long  values[16]

PRI changevalue(i, x)

  sum += x-values[i]
  values[i] := x

  return sum

coryco2

Thanks; much appreciated!