Comparing numbers
- Rust course
- Beginner
- Lesson 62/115
- 6 min
Parse the guess into a number and compare with Ordering.
Converting to a number
parse is used to turn text into a number; the target type must be given. The result is a Result because texts like "abc" can't be converted:
let tahmin: u32 = tahmin.trim().parse().expect("Bir sayı yaz!");Here the old tahmin (a String) is shadowed by a new u32 with the same name; there's no need to invent another name.
cmp and Ordering
a.cmp(&b) returns one of three values of the type std::cmp::Ordering: Less, Greater, Equal. match forces you to handle all three:
use std::cmp::Ordering;
match tahmin.cmp(&gizli) {
Ordering::Less => println!("Çok küçük"),
Ordering::Greater => println!("Çok büyük"),
Ordering::Equal => println!("Bildin!"),
}If you forget an arm, the compiler gives a "non-exhaustive patterns" error.
Practice First comparison
Convert the text "30" with parse::<u32>() (unwrap) and compare it with let gizli: u32 = 42; using cmp. Print 30: Çok küçük for Less, Çok büyük for Greater and Bildin! for Equal.
Starter code
use std::cmp::Ordering;
fn main() {
// buraya yaz
}Sample solution
use std::cmp::Ordering;
fn main() {
let gizli: u32 = 42;
let tahmin: u32 = "30".parse().unwrap();
match tahmin.cmp(&gizli) {
Ordering::Less => println!("{}: Çok küçük", tahmin),
Ordering::Greater => println!("{}: Çok büyük", tahmin),
Ordering::Equal => println!("{}: Bildin!", tahmin),
}
}Expected output
30: Çok küçük
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does <code>"-5".parse::<u32>()</code> return?
- Err(...) Correct answer
- Ok(5)
- Ok(-5)
- Panic
Explanation: u32 is unsigned; the minus sign is an invalid digit and Err is returned.
2 Compare
match tahmin.____(&gizli) {
Ordering::Less => println!("Çok küçük"),
Ordering::Greater => println!("Çok büyük"),
Ordering::Equal => println!("Bildin!"),
}match tahmin.cmp(&gizli) {
Ordering::Less => println!("Çok küçük"),
Ordering::Greater => println!("Çok büyük"),
Ordering::Equal => println!("Bildin!"),
}Explanation: cmp returns an Ordering value.
3 cmp result
| Term | Meaning |
|---|---|
3.cmp(&5) |
Less |
5.cmp(&3) |
Greater |
5.cmp(&5) |
Equal |
"x".parse::<u32>() |
Err |