CodeBlanks Logo Icon CodeBlanks
Login Register

Expressions and statements

Learn the difference between expressions and statements.

Expressions and statements

In Rust a statement does something but produces no value (let x = 5;); an expression produces a value (5 + 1, kare(3), if ..., { ... }). Putting a semicolon after an expression turns it into a statement.

let y = {
    let x = 3;
    x + 1        // the block's value: 4
};
println!("{y}");

That's why let x = (let y = 6); is invalid: let doesn't produce a value.

match is an expression too

To classify a value and assign the result directly to a variable, a match expression is used:

let puan = 72;
let harf = match puan {
    90..=100 => 'A',
    70..=89 => 'B',
    50..=69 => 'C',
    _ => 'F',
};
println!("{harf}");   // B

Every arm must return the same type; otherwise the compiler reports an error.

Practice Letter grade

Write the fn harf(puan: u32) -> char function with a match expression: 90–100 'A', 70–89 'B', 50–69 'C', otherwise 'F'. Print harf(95), harf(72) and harf(30) on one line.

Starter code

main.rs
fn main() {
    // buraya yaz
}

Sample solution

main.rs
fn harf(puan: u32) -> char {
    match puan {
        90..=100 => 'A',
        70..=89 => 'B',
        50..=69 => 'C',
        _ => 'F',
    }
}

fn main() {
    println!("{} {} {}", harf(95), harf(72), harf(30));
}

Expected output

A B F

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which of these is an expression?

  • fn f() {}
  • use std::io;
  • { let a = 2; a * a } Correct answer
  • let a = 2;

Explanation: The block produces the value of its last expression (4); the others are declarations and statements that produce no value.

2 if as an expression

Question 
let durum = ____ yas >= 18 { "yetişkin" } else { "çocuk" };
Answer 
let durum = if yas >= 18 { "yetişkin" } else { "çocuk" };

Explanation: if is an expression; the chosen arm's value is assigned directly to the variable.

3 Code and kind

Term Meaning
let x = 5; Statement
5 + 1 Expression
{ x + 1 } A value-producing block
x + 1; A statement discarding the value

All lessons in Beginner

1 Rust basics

  1. What is Rust?
  2. Project with Cargo
  3. Your first program
  4. println! and formatting
  5. Comments
  6. Summary - Rust basics

2 Variables

  1. Variables with let
  2. Mutability with mut
  3. Constants with const
  4. Static variables
  5. Shadowing
  6. Summary - Variables

3 Data types

  1. Integers
  2. Floating point
  3. Bool and char
  4. Tuple
  5. Array
  6. Summary - Data types

4 Strings

  1. &str vs String
  2. Creating a String
  3. Concatenating strings
  4. format! macro
  5. String length
  6. Summary - Strings

5 Project: Calculator

  1. Project skeleton
  2. Reading input
  3. Computing
  4. Error handling
  5. Loop and exit

6 Functions

  1. Defining with fn
  2. Parameters
  3. Return value
  4. Expressions and statements
  5. Early return
  6. Summary - Functions

7 Control flow

  1. if-else
  2. match basics
  3. loop
  4. while loop
  5. for loop
  6. Summary - Control flow

8 Ownership

  1. What is ownership?
  2. Move semantics
  3. Copy trait
  4. Functions and ownership
  5. Return and ownership
  6. Summary - Ownership

9 Borrowing

  1. References
  2. Mutable reference
  3. Borrowing rules
  4. Dangling reference
  5. References and functions
  6. Summary - Borrowing

10 Slices

  1. String slices
  2. Slice syntax
  3. Array slices
  4. Slices and functions
  5. Range types
  6. Summary - Slices

11 Project: Guessing game

  1. Game skeleton
  2. Reading input
  3. Comparing numbers
  4. Random number
  5. Loop and exit

12 Structs

  1. Struct definition
  2. Creating an instance
  3. Tuple struct
  4. Unit-like struct
  5. Field update
  6. Summary - Structs

13 Methods

  1. impl block
  2. self parameter
  3. &mut self
  4. Associated functions
  5. Multiple impl blocks
  6. Summary - Methods

14 Enums

  1. Enum definition
  2. Variants
  3. Variants with data
  4. Option<T>
  5. Option instead of null
  6. Summary - Enums

15 Pattern matching

  1. match patterns
  2. Value binding
  3. if let
  4. while let
  5. _ wildcard
  6. Summary - Pattern matching

16 Project: To-do CLI

  1. Task model
  2. Adding
  3. Listing
  4. Marking done
  5. Reading commands

17 Vectors

  1. Vec<T>
  2. Push and pop
  3. Index and get
  4. Looping a vector
  5. with_capacity
  6. Summary - Vectors

18 Advanced strings

  1. String and &str conversion
  2. chars and bytes
  3. Slicing strings
  4. contains and replace
  5. split and join
  6. Summary - Advanced strings

19 Error handling

  1. Result<T, E>
  2. panic!
  3. ? operator
  4. match and Result
  5. unwrap and expect
  6. Summary - Error handling

20 Beginner final

  1. Vowel counter
  2. Average calculator
  3. Bank account
  4. Temperature converter