Why does this program giving me unexpected behaviour [duplicate] - rust

Question

This question already has an answer here:
Why is my code failling in Rust when I don't declare a variable in the loop
(1 answer)
Closed 5 months ago.
I've just finished the 4th chapter of 'The Book'. To test my knowledge I was building this little project. But, for some reason I/O is not working the way I'm expecting. I was trying to figure out problem of my code, but could not. I'd really appriciate if someone can tell what the problem is.
here's the code:
use std::{
io::{stdin, stdout, Write},
vec,
};
fn main() {
let mut db: Vec<String> = vec![];
let mut key = String::new();
let mut value = String::new();
let mut operation = String::new();
let operations = (
String::from("put"),
String::from("get"),
String::from("exit"),
);
println!(
"\n\tyour options are {}, {}, {}.\n",
operations.0, operations.1, operations.2
);
loop {
println!("what do you wanna do?");
stdin()
.read_line(&mut operation)
.expect("colud not parse input");
let operation = operation.trim();
if operation == operations.0 {
println!("enter your key");
stdin()
.read_line(&mut key)
.expect("could not parse the input");
let key = key.trim();
println!("enter your value");
stdin()
.read_line(&mut value)
.expect("could not parse the input");
let value = value.trim();
store(&mut db, &key, &value);
println!("\n\tvalue `{1}` stored to key `{0}`\n", key, value);
} else if operation == operations.1 {
println!("enter your key");
stdin()
.read_line(&mut key)
.expect("could not parse the input");
let key = key.trim();
println!("\n\tthe value of {} is {}\n", key, get(&mut db, &key));
} else if operation == operations.2 {
break;
} else {
println!("\n\t{} is not a valid option\n", operation);
}
stdout().flush().unwrap();
}
}
fn store(db: &mut Vec<String>, key: &str, value: &str) {
let new_data = format!("{},{}", key, value);
db.push(new_data);
}
fn get(db: &mut Vec<String>, key: &str) -> String {
for data in db {
if data.split(',').next().expect("error while parsing the key") == key {
return data
.split(',')
.next()
.expect("error while parsing the value")
.to_string();
}
}
String::from("404")
}
output:
your options are put, get, exit.
what do you wanna do?
put
enter your key
name
enter your value
cob
value `cob` stored to key `name`
what do you wanna do?
exit
put
exit is not a valid option
what do you wanna do?
exit
put
exit
exit is not a valid option

Answer 1

You need to look at the documentation of what read_line actually does:
Locks this handle and reads a line of input, appending it to the specified buffer.
Meaning, it doesn't replace the content of operation, it appends to it.
There are two possible easy fixes:
clear operation before reading
don't keep operation between iterations
I'd go with #2, as I think there is no reason why operation is defined outside of the loop.
use std::{
io::{stdin, stdout, Write},
vec,
};
fn main() {
let mut db: Vec<String> = vec![];
let mut key = String::new();
let mut value = String::new();
let operations = (
String::from("put"),
String::from("get"),
String::from("exit"),
);
println!(
"\n\tyour options are {}, {}, {}.\n",
operations.0, operations.1, operations.2
);
loop {
println!("what do you wanna do?");
let mut operation = String::new();
stdin()
.read_line(&mut operation)
.expect("colud not parse input");
let operation = operation.trim();
if operation == operations.0 {
println!("enter your key");
stdin()
.read_line(&mut key)
.expect("could not parse the input");
let key = key.trim();
println!("enter your value");
stdin()
.read_line(&mut value)
.expect("could not parse the input");
let value = value.trim();
store(&mut db, &key, &value);
println!("\n\tvalue `{1}` stored to key `{0}`\n", key, value);
} else if operation == operations.1 {
println!("enter your key");
stdin()
.read_line(&mut key)
.expect("could not parse the input");
let key = key.trim();
println!("\n\tthe value of {} is {}\n", key, get(&mut db, &key));
} else if operation == operations.2 {
break;
} else {
println!("\n\t{} is not a valid option\n", operation);
}
stdout().flush().unwrap();
}
}
fn store(db: &mut Vec<String>, key: &str, value: &str) {
let new_data = format!("{},{}", key, value);
db.push(new_data);
}
fn get(db: &mut Vec<String>, key: &str) -> String {
for data in db {
if data.split(',').next().expect("error while parsing the key") == key {
return data
.split(',')
.next()
.expect("error while parsing the value")
.to_string();
}
}
String::from("404")
}