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Average calculator

Write and test a function that computes the average of a Vec.

Final task: average

You'll write a function that computes the average of a list of grades. The average of an empty list is undefined; return Option<f64> to express this honestly:

fn ortalama(notlar: &[f64]) -> Option<f64> {
    if notlar.is_empty() {
        return None;
    }
    let mut toplam = 0.0;
    for n in notlar {
        toplam += n;
    }
    Some(toplam / notlar.len() as f64)
}

notlar.len() is a usize; it's converted with as f64 to divide by an f64.

Short form with iterators

The same calculation shrinks to one line with iterator methods:

let toplam: f64 = notlar.iter().sum();
let en_yuksek = notlar.iter().cloned().fold(f64::MIN, f64::max);

When printing the average, the {:.1} format shows one decimal place. Handle the result with match and give a meaningful message for an empty list.

Practice Grade average

Write the ortalama function above. Handle the result for [72.5, 88.0, 91.5] and an empty slice with match: print Ortalama: 84.0 ({:.1}) or Not yok.

Starter code

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

Sample solution

main.rs
fn ortalama(notlar: &[f64]) -> Option<f64> {
    if notlar.is_empty() {
        return None;
    }
    let mut toplam = 0.0;
    for n in notlar {
        toplam += n;
    }
    Some(toplam / notlar.len() as f64)
}

fn main() {
    let dolu = vec![72.5, 88.0, 91.5];
    let bos: Vec<f64> = Vec::new();
    for liste in [&dolu, &bos] {
        match ortalama(liste) {
            Some(o) => println!("Ortalama: {:.1}", o),
            None => println!("Not yok"),
        }
    }
}

Expected output

Ortalama: 84.0
Not yok

Questions and answers

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

1 If <code>toplam / 0.0</code> were computed for an empty list, what would the result be?

  • 0.0
  • Compile error
  • NaN (0.0 / 0.0) Correct answer
  • Panic

Explanation: Floating-point division by zero doesn't panic; it produces NaN, which spreads silently. Option avoids this trap.

2 Convert the type

Question 
Some(toplam / notlar.len() ____)
Answer 
Some(toplam / notlar.len() as f64)

Explanation: A usize value is converted with as f64 to divide by an f64.

3 Input and average result

Term Meaning
[72.5, 88.0, 91.5] Some(84.0)
[] None
[10.0] Some(10.0)
[1.0, 2.0] Some(1.5)

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