Introduction to Julia Programming: Text Foundations: Chars vs Strings in Julia

In Julia, text is handled via two distinct architectural entities: the 32-bit Char primitive and the immutable, UTF-8 encoded String. Unlike languages where a character is a one-length string, Julia treats Char as a first-class numeric type representing a Unicode code point.

1. Type Hierarchy & Memory

Concrete Char is a $32$-bit primitive type (subtype of AbstractChar). The built-in String (subtype of AbstractString) supports the full Unicode range. While a Char is fixed-size, String is variable-width; individual characters take 1 to 4 bytes, with the transition point for ASCII occurring at $0x80(128)$.

2. Arithmetic & Comparison

Since Char represents a numeric code point, you can perform arithmetic. Use Int('a') to get 97 and Char(97) to get 'a'. Lexicographical comparisons are supported: 'X' < 'x' is true because uppercase precedes lowercase in Unicode.

Feature	Char (`'a'`)	String (`"a"`)
Type	`Char`	`String`
Size	Fixed $32$-bit	Variable UTF-8
Mutable	N/A (Value Type)	No (Immutable)

Chained comparisons like 'A' <= 'X' <= 'Y' evaluate to true or false based on the Unicode sequence.

TERMINAL bash — 80x24

> Ready. Click "Run" to execute.

QUESTION 1

What is the size of a single Char in Julia?

8-bit

16-bit

32-bit

Variable (1-4 bytes)

QUESTION 2

Which of the following creates a String, not a Char?

'a'

"Julia"

Char(97)

'\u2200'

QUESTION 3

What is the result of 'a' + 1 in Julia?

'b'

"a1"

An Error

QUESTION 4

True or False: Julia Strings are mutable.

True

False

❌ Incorrect

Attempting s[1] = 'x' will result in an error.

QUESTION 5

Which abstract type do all Julia strings inherit from?

AbstractChar

BaseString

AbstractString

UnicodeString

✅ Correct!

All string types are subtypes of AbstractString.

Case Study: Caesar Cipher Logic

Character Manipulation & Validation

You are implementing a rotation cipher. You need to convert a character to its integer code, perform a shift, and handle validation check boundaries.

How would you explicitly convert the character 'z' to its numeric Unicode value and back to a character?

Solution:
Use Int('z') to obtain the integer code point, and Char(val) to convert an integer back to a character.

If you have a character variable c, how do you verify if it is an uppercase letter between 'A' and 'Y' using a single expression?

Solution:
Use chained comparison: 'A' <= c <= 'Y'. This checks the lexicographical order based on Unicode values.

Why would text = "Hello"; text[1] = 'h' fail, and how should you achieve the change instead?

Solution:
It fails because Strings are immutable. You must create a new string, for example using concatenation: "h" * text[2:end] or string interpolation.