Summing and Averaging an Array

To sum an array you need one variable outside the loop, usually called sum, started at 0. The loop visits each index from 0 to arr.length - 1, and each pass does sum = sum + arr[i]. That variable is an accumulator: it carries the running total forward from one iteration to the next, so by the time the loop ends it holds the total of every element. The count is just arr.length, no loop needed, since arrays know their own size.

The average needs both pieces: the sum tells you the total, but the total alone is meaningless without knowing how many numbers produced it. 400 split across 4 scores averages to 100; the same 400 split across 8 scores averages to 50. So average = sum / count, but the division has to be done carefully. If sum and count are both int, Java performs integer division first, truncating any decimal part, and only afterward stores that truncated whole number into a double. Casting happens too late to help. The fix is forcing double division before the assignment, by casting one operand: (double) sum / count.

This same accumulator pattern — initialize before the loop, update inside it — is exactly what comes next for finding a maximum, counting matches, or filtering elements, like skipping negatives when averaging. Only the update line changes; the shape of the loop stays the same.