Totalling & counting

Totalling: a running total

• Totalling adds up a series of numbers.
• Start a total at 0, then add each value to it.
• The pattern total = total + value is called an accumulator.

nums = [10, 20, 30]
total = 0
for n in nums:
    total = total + n
print(total)        # 60

Counting: a running count

• Counting tallies how many values meet a rule.
• Start a count at 0, then add 1 each time the rule is true.

nums = [4, -2, 7, -5]
count = 0
for n in nums:
    if n > 0:
        count = count + 1
print(count)        # 2

Average = total ÷ count

• An average is the total divided by how many values there are.
• len(nums) gives the number of items in a list.

nums = [2, 4, 6]
average = sum(nums) / len(nums)
print(average)      # 4.0

In the exam: standard methods

• Totalling and counting are named standard methods in the syllabus.

Total ← 0
FOR i ← 1 TO 5
    Total ← Total + Number[i]
NEXT i

Common mistakes

• Set the total to 0 before the loop, then add to it inside.
• A counter starts at 0 and goes up by 1 each time.
• Do not reset the total inside the loop.

Now you try

• Use a loop with a running total or count.
• Press Check answer to test your code.