fn math(s: &str) -> i32 {
    // remove whitespace characters so all we have left are digits and the operator
    let math_str: String = s.chars().filter(|ch| !ch.is_whitespace()).collect();
    
    // find the position of the operator character
    let pos: usize = math_str    
        .chars()
        .position(|ch| match ch {
            '+' | '-' | '*' | '/' | '=' => true,
            _ => false
        })
        .expect("invalid operator, expected +, -, *, / or =");
    
    // extract the two numbers from the string
    let num1: i32 = math_str[..pos].parse().unwrap();
    let num2: i32 = math_str[pos + 1..].parse().unwrap();
    
    match &math_str[pos..=pos] {
        "+" => num1 + num2,
        "-" => num1 - num2,
        "*" => num1 * num2,
        "/" => num1 / num2,
        _ => (num1 == num2) as i32,
    }
}