Length and Character Iteration

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.len() returns the number of bytes in the string, not the number of Unicode characters. For pure ASCII text the values are the same; accented characters or emoji may occupy more than one byte.

.chars() returns a string array — each element is a character (a string of length 1). Iterate with for to process letter by letter:

.len() for measuring; .chars() for iterating and counting occurrences.

08-len-and-chars.zolo

Playground

// Feature: Length and iteration over characters

// Syntax: `s.len()` -> int, `s.chars()` -> [str]

// When to use: measure length, iterate character by character.


// -- len: byte length ------------------------------------------

print("zolo".len())  // 4

print("".len())  // 0

print("hello world".len())  // 11


// Note: `.len()` returns the length in BYTES, not Unicode code

// points. Accented characters / emoji may take more than one byte.

print("cafe".len())  // 4 (plain ASCII)

print("a".len())  // 1


// -- chars: array of characters (1 string per element) --------

let cs = "abc".chars()
print(cs.len())  // 3

print(cs[0])  // a

print(cs[1])  // b

print(cs[2])  // c


// Iterate character by character.

for c in "zolo".chars() {
  print(c)
}

// expected:

// z

// o

// l

// o


// Count occurrences of a character.

fn count_char(s: str, target: str) -> int {
  var total = 0
  for c in s.chars() {
    if c == target {
      total = total + 1
    }
  }
  return total
}

print(count_char("mississippi", "s"))  // 4

print(count_char("zolo lang", "o"))  // 2


// Check whether a string is "empty".

fn is_empty(s: str) -> bool {
  return s.len() == 0
}

print(is_empty(""))  // true

print(is_empty("x"))  // false

Challenge

Write a function reverse(s: str) -> str that walks .chars() backwards (use a decreasing index) and accumulates the characters with +. Test with "zolo" — the result should be "oloz".