How to overwrite mutable string inside a loop? - rust

Question

My example is slightly modified from the guessing game tutorial in The Rust Book.
After the first iteration, the loop does not appear to read in the user input to the mutable string correctly.
Can you please identify what is wrong in the below code with regards to mut input_text?
extern crate rand;
use rand::Rng;
use std::cmp::Ordering;
use std::io;
fn main() {
let random_number = rand::thread_rng().gen_range(1, 51);
let mut input_text = String::new(); // Works fine if allocated inside loop
loop {
println!("Enter your guess:");
io::stdin()
.read_line(&mut input_text)
.expect("Failed to read input");
let input_number: u32 = match input_text.trim().parse() {
Ok(num) => num,
Err(_) => continue,
};
println!(
"You entered {} which converted to u32 is {}",
input_text, input_number
);
match input_number.cmp(&random_number) {
Ordering::Greater => println!("Input > Random"),
Ordering::Less => println!("Input < Random"),
Ordering::Equal => println!("Input == Random"),
}
}
}

Answer 1

As #Jmb mentioned in the comments, read_line doesn't overwrite the String but appends to it. If you'd like to overwrite the String you have to first call clear on it like so:
use rand::Rng;
use std::cmp::Ordering;
use std::io;
fn main() {
let random_number = rand::thread_rng().gen_range(1, 51);
let mut input_text = String::new();
loop {
println!("Enter your guess:");
// clear input_text from previous loop iteration
input_text.clear();
io::stdin()
.read_line(&mut input_text)
.expect("Failed to read input");
let input_number: u32 = match input_text.trim().parse() {
Ok(num) => num,
Err(_) => continue,
};
println!(
"You entered {} which converted to u32 is {}",
input_text.trim(), input_number
);
match input_number.cmp(&random_number) {
Ordering::Greater => println!("Input > Random"),
Ordering::Less => println!("Input < Random"),
Ordering::Equal => {
println!("Input == Random");
break; // break on win condition
},
}
}
}
Also your program was an infinite loop so I added a break on the win condition.