Sums, counts, and extrema

After loops, you can process many inputs while keeping only a total, a counter, or the best value seen so far. Each input is examined once; the whole sequence need not be stored.

Sum and count selected values#

Initialize the sum and counter to zero. Check the required property for each input and update both variables only when it holds.

1n = 52sum = 03count = 04FOR i FROM 1 TO n5  INPUT x6  IF x MOD 2 == 0 THEN7    sum = sum + x8    count = count + 19  END10END11PRINT sum12PRINT count

For inputs 3, 8, -2, 5, 0, the selected numbers are 8, -2, 0. Their sum is 6 and their count is 3. Zero increases the count even though it leaves the sum unchanged.

After each iteration, the sum equals the total of the even numbers read so far. Such a property, preserved between iterations, is called an invariant. It explains why the final answer is correct.

Maximum#

Starting a maximum at zero fails when every input is negative. Read the first value separately and make it the initial candidate.

1n = 42INPUT maximum3FOR i FROM 2 TO n4  INPUT x5  IF x > maximum THEN6    maximum = x7  END8END9PRINT maximum

For -9, -4, -12, -7, the maximum is -4. This algorithm requires n >= 1. An empty sequence has no maximum and needs separate handling. Replace > with < to find a minimum.

Product and average#

Multiplication has neutral element 1; a product initialized to 0 stays zero. The average of selected values is sum / count only when count > 0. Distinguish the number of all inputs from the number that satisfy your condition.

A traversal takes O(n) time and O(1) extra memory: the number of variables does not grow with the input count. MiniScript+ does not currently provide arrays; these patterns process values as they arrive.

Practice#

1. Count strictly positive values. For -2, 0, 5, 7, the answer is 2.
2. Find the minimum and its frequency. For 4, 1, 3, 1, report 1 and 2.
3. Average the even inputs, handling the case where none exist. Test one value, all-negative values, and repeated values.