CodeBlanks Logo Icon CodeBlanks
Login Register

Floating point

Learn the f32 and f64 floating-point types.

Floating-point numbers

Rust has two floating-point types: f32 (single precision) and f64 (double precision, the default). On modern CPUs f64 is nearly as fast and more precise.

let pi = 3.14159;          // f64
let yaricap: f32 = 2.0;
let alan = pi * 2.0 * 2.0;
println!("{:.2}", alan);    // 12.57

Integers and decimals can't be mixed directly: 2 * 1.5 compiles (literals) but n * 1.5 (n: i32) needs n as f64 * 1.5.

Comparing decimals

Because decimals are stored in binary, 0.1 + 0.2 == 0.3 is false. Comparison is done with a tolerance:

let a = 0.1 + 0.2;
println!("{}", a == 0.3);                    // false
println!("{}", (a - 0.3).abs() < 1e-10);    // true

f64::NAN isn't even equal to itself; that's why floats don't implement Eq and Ord, and total_cmp is used to sort them.

Practice Circle area

Declare let r: i32 = 3;. Compute the area with std::f64::consts::PI * (r as f64).powi(2) and print it with {:.2}.

Starter code

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

Sample solution

main.rs
fn main() {
    let r: i32 = 3;
    let alan = std::f64::consts::PI * (r as f64).powi(2);
    println!("{:.2}", alan);
}

Expected output

28.27

Questions and answers

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

1 Why doesn't <code>let n: i32 = 3; let x = n * 1.5;</code> compile?

  • An i32 can't be multiplied by an f64; n as f64 is needed Correct answer
  • 1.5 is invalid
  • n is immutable
  • It compiles

Explanation: Rust doesn't convert implicitly between number types; an explicit conversion is written with as.

2 Type conversion

Question 
let adet: i32 = 4;
let toplam = adet ____ f64 * 2.5;
Answer 
let adet: i32 = 4;
let toplam = adet as f64 * 2.5;

Explanation: The as keyword converts explicitly between numeric types.

3 Expression and result

Term Meaning
7.0 / 2.0 3.5
7 / 2 3 (integer)
0.1 + 0.2 == 0.3 false
2.0_f64.sqrt() 1.414...

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