How to combine if let match expression in rust

//here is my code. It is a Temperature Converter that takes input for Kelvin, Celsius or Fahrenheit and outputs converted value for corresponding contrary units.

// Problem:

// it will ask value first, which must be number, so the loop restarts. this is OK
// it will then ask for unit, which must be k,c or f. Upon different entry, it does catches and print "input k for kelvin, c for celcius F for Fahrenheit"
// But input doesnot register and jumps to the begening of the loop asking for value in numbers.

//All in all i want to catch the unit variable with k,c or f else ask the user to do so, not jump to the begening of loop.

// i am learning rust so excuse me for anything out of the norm.

//Here is my main.rs:

fn main() {
println!("\nWelcome. This is Temperature-Converter\n");
println!("I work with Fahrenheit, Celsius and Kelvin");
println!("\nPlease Input the Value you want to convert: ");
loop{    
let mut value = String::new();
std::io::stdin().read_line(&mut value).expect("Failed to read line");
let value:f32 = match value.trim().parse(){
Ok(num) => num,
Err(_) => {
println!("please input value in number(s).");
continue;
}
};
println!("Thank You, I have the value: {value}.\nPlease provide it's respective unit of measurement.");
println!("K : for Kelvin    C : for Celsius     F : for Fahrenheit : ");
let mut unit = String::new();
std::io::stdin().read_line(&mut unit).expect("Failed to read line");
let unit = unit.trim().to_uppercase();
let unit = match unit.as_str() {
"K"=>"K",
"F"=>"F",
"C"=>"C",
_=>{
println!("please input K, F or C for Kelvin, Fahrenheit or Celcius respectively.");
continue;
}
};
println!("Thank you for your input. I see that you want to convert {value} degree {unit}.");
println!("Please wait while i provide all possible conversions.\nThis will be quick.");
if unit == "K"{
let value_c = value-273.15;
let value_f = (((value-273.15)*9.0)+(32.0*5.0))/5.0;
println!("{value}{unit} is converted to: {value_c}C and {value_f}F");
println!("Thank You for using Temperature Conversior. It was a pleasure to assist you. Byee!!");
break;
}
else if unit == "C"{
let value_k = value+273.15;
let value_f = (value*(9.0/5.0))+32.0;
println!("{value}{unit} is converted to:{value_k}K and {value_f}F");
println!("Thank You for using Temperature Conversior. It was a pleasure to assist you. Byee!!");
break;
}
else if unit == "F"{
let value_k = (((value-32.0)*5.0)/9.0)+273.15;
let value_c = ((value-32.0)*5.0)/9.0;
println!("{value}{unit} is Converted to: {value_k}K and {value_c}C");
println!("Thank You for using Temperature-Converter. It was a pleasure to assist you. Byee!!");
break;
};
}
}

//i tried :

if let unit = match unit.as_str() {
"K"=>"K",
"F"=>"F",
"C"=>"C",
_=>{println!("please input K, F or C for Kelvin, Fahrenheit or Celcius respectively.")}
};

// In fact i am having hard time understanding "match" and scope and return value of "loop"

The program logic can still be simplified, for now only the syntactical problems are dealt with here:

fn main() {
println!("\nWelcome. This is Temperature-Converter\n");
println!("I work with Fahrenheit, Celsius and Kelvin");
println!("\nPlease Input the Value you want to convert: ");
loop {
let mut input = String::new();
let mut value = 0.0_f32;
match std::io::stdin().read_line(&mut input) {
Ok(_) => {
value = match input.trim().parse() {
Ok(num) => num,
Err(_) => {
println!("please input value in number(s).");
continue;
}
};
println!("Thank You, I have the value: {value}.");
}
Err(_) => println!("Failed to read line"),
}
println!("Please provide it's respective unit of measurement.");
println!("K: for Kelvin    C: for Celsius     F: for Fahrenheit : ");
let mut unit;
loop {
unit = String::new();
match std::io::stdin().read_line(&mut unit) {
Ok(_) => {
unit = unit.trim().to_uppercase();
match unit.as_str() {
"K" | "F" | "C" => break,
_ => println!("please input K, F or C for Kelvin, Fahrenheit or Celcius respectively."),
}
}
Err(_) => println!("Failed to read line"),
}
}
println!("Thank you for your input. I see that you want to convert {value} degree {unit}.");
println!("Please wait while i provide all possible conversions.\nThis will be quick.");
if unit == "K" {
let value_c = value - 273.15;
let value_f = (((value - 273.15) * 9.0) + (32.0 * 5.0)) / 5.0;
println!("{value}{unit} is converted to: {value_c}C and {value_f}F");
println!("Thank You for using Temperature Conversior. It was a pleasure to assist you. Byee!!");
break;
} else if unit == "C" {
let value_k = value + 273.15;
let value_f = (value * (9.0 / 5.0)) + 32.0;
println!("{value}{unit} is converted to:{value_k}K and {value_f}F");
println!("Thank You for using Temperature Conversior. It was a pleasure to assist you. Byee!!");
break;
} else if unit == "F" {
let value_k = (((value - 32.0) * 5.0) / 9.0) + 273.15;
let value_c = ((value - 32.0) * 5.0) / 9.0;
println!("{value}{unit} is Converted to: {value_k}K and {value_c}C");
println!("Thank You for using Temperature-Converter. It was a pleasure to assist you. Byee!!");
break;
};
}
}

Thanks for to user: Kaplan
i have just defined variables with loop and later break the loop with variable value out of the loop.

fn main() {
println!("\nWelcome. This is Temperature-Converter\n");
println!("I work with Fahrenheit, Celsius and Kelvin");
println!("\nPlease Input the Value you want to convert: ");
let value:f32 = loop{
let mut value = String::new();
std::io::stdin()
.read_line(&mut value)
.expect("Failed to read line");
match value.trim().parse::<f32>(){
Ok(num) => break num,
Err(_) => {
println!("please input value in number(s).");}
};
};
println!("Thank You, I have the value: {value}.\nPlease provide it's respective unit of measurement.");
println!("K : for Kelvin    C : for Celsius     F : for Fahrenheit : ");
let unit = loop{
let mut unit = String::new();
std::io::stdin()
.read_line(&mut unit)
.expect("Failed to read line");
let unit = unit.trim().to_uppercase();
match &*unit{
"K" | "F" | "C" => break unit,
_=>{
println!("Please input K, F or C for Kelvin, Fahrenheit or Celsius respectively.\nI am not case sensitive.");
}
};
};
if unit == "K"{
let value_c = value-273.15;
let value_f = (((value-273.15)*9.0)+(32.0*5.0))/5.0;
println!("{value}{unit} is converted to: {value_c}C and {value_f}F");
println!("Thank You for using Temperature Conversior. It was a pleasure to assist you. Byee!!");
}
else if unit == "C"{
let value_k = value+273.15;
let value_f = (value*(9.0/5.0))+32.0;
println!("{value}{unit} is converted to:{value_k}K and {value_f}F");
println!("Thank You for using Temperature Conversior. It was a pleasure to assist you. Byee!!");
}
else if unit == "F"{
let value_k = (((value-32.0)*5.0)/9.0)+273.15;
let value_c = ((value-32.0)*5.0)/9.0;
println!("{value}{unit} is Converted to: {value_k}K and {value_c}C");
println!("Thank You for using Temperature-Converter. It was a pleasure to assist you. Byee!!");
};
}