let v: Vec<u8>: v = Vec::new();
let v = vec![1,2,3,4];//注意小写v
v.push(1);
let third: &i32 = &v[2];//访问越界，panic
v.get(2);//注意空情况，一般用match
for i in &v {
    println!("{}",i);
}
for i in &mut v {
    *i += 100;
}