Goal: Visit each character of a string and count the vowels.

A string is a row of letters

Every message you type, every name in your contacts, is a string: a row of characters, one per box, numbered from 0 just like an array. "cat" has 3 boxes: c in box 0, a in box 1, t in box 2.

A space is a character too, and it takes a box. So "hi there" has 8 characters, not 7. Punctuation and digits count the same way.

One character per box: numbered from 0.

Spaces count: they take a box like any letter.

s = "sunny day" (␣ is the space)

␣

count: 0

Box 0 holds 's'. Not a vowel. Just like an array, we look at one box at a time.

Move 1 of 6

Everything from arrays still works

Walking a string is walking an array: visit each box from the first to the last, and do something with the character you find. Counting vowels is the counting loop you already know, with a new question at each box: is this character one of a, e, i, o, u?

An empty string has no boxes, so the loop doesn't run and the count stays 0.

Same loop: a new question at each box.

In code

count = 0
for ch in s:
    if ch == " ":
        count += 1