Convert a String to int?

let my_u8: u8 = "42".parse().unwrap();
let my_u32: u32 = "42".parse().unwrap();

// or, to be safe, match the `Err`
match "foobar".parse::<i32>() {
  Ok(n) => do_something_with(n),
  Err(e) => weep_and_moan(),
}

str::parse::<u32> returns a Result<u32, core::num::ParseIntError> and Result::unwrap "Unwraps a result, yielding the content of an Ok [or] panics if the value is an Err, with a panic message provided by the Err's value."

str::parse is a generic function, hence the type in angle brackets.

If you get your string from stdin().read_line, you have to trim it first.

let my_num: i32 = my_num.trim().parse()
   .expect("please give me correct string number!");

You can directly convert to an int using the str::parse::<T>() method, which returns a Result containing the int.

let my_string = "27".to_string();  // `parse()` works with `&str` and `String`!
let my_int = my_string.parse::<i32>().unwrap();

You can either specify the type to parse to with the turbofish operator (::<>) as shown above or via explicit type annotation:

let my_int: i32 = my_string.parse().unwrap();

Since parse() returns a Result, it will either be an Err if the string couldn't be parsed as the type specified (for example, the string "peter" can't be parsed as i32), or an Ok with the value in it.