fn main() {
    // integer to string
    let num = 123;
    let s = num.to_string();
    println!("s is {}", s); 

    // string to integer
    let num2 = s.parse::<i32>().unwrap();
    println!("num2 is {}", num2);

    // join
    let strlist = vec!["hello", "world", "from", "rust"];
    println!("joined: {}", strlist.join(", "));

    // trim
    let s = "  Hello world  ";
    println!("trimmed: {} length: {}", s.trim(), s.trim().len());

    // to lowercase
    println!("lowercase: {}", s.to_lowercase());

    // to upppercase
    println!("uppercase: {}", s.to_uppercase());

    // find
    println!("find e: {:?}", s.find("e"));
    println!("find d: {:?}", s.find("d"));
    println!("find z: {:?}", s.find("z"));

    // start & end with
    let s = s.trim().to_lowercase();
    println!("starts with: {}", s.starts_with("he"));
    println!("ends with: {}", s.ends_with("ld"));

    // replace
    println!("replaced: {}", s.replace(" ", "##"));

    // split
    let splitted: Vec<&str> = s.split(" ").collect();
    println!("Splitted: {:?}", splitted);
}

s is 123
num2 is 123
joined: hello, world, from, rust
trimmed: Hello world length: 11
lowercase:   hello world  
uppercase:   HELLO WORLD  
find e: Some(3)
find d: Some(12)
find z: None
starts with: true
ends with: true
replaced: hello##world
Splitted: ["hello", "world"]