Counters

Counters

In this tutorial, we'll update a value each time a loop runs.

A counter is a variable that changes by a regular amount each time a loop runs.

count = 0

while count < 5:
    print(count)
    count = count + 1

The line count = count + 1 is what moves the loop forward.

Counting Up

number = 1

while number <= 5:
    print(number)
    number = number + 1

Output:

1
2
3
4
5

Counting Down

timer = 5

while timer > 0:
    print(timer)
    timer = timer - 1

print("Go")

Counting Matches

Counters can track things:

word = "banana"
index = 0
count_a = 0

while index < len(word):
    if word[index] == "a":
        count_a = count_a + 1
    index = index + 1

print(count_a)

This is more complex than a for loop version, but it shows how counters control positions.

Shorter Updates

Python also supports a shorter way to add one:

count = count + 1
count += 1

Both lines mean the same thing. Beginners may find the first version clearer at first, and that is completely fine.

Practice

Use a counter to print every number from 10 down to 1.