running many lines of ocaml code on vscode

I just started learning ocaml and I have a problem with my vscode.

I noticed that when i write too many lines of codes they won't be compiled, only some of them. For example in the 1st picture, it only gives the result of the 3 first lines, then for the variable "t" it doesn't do anything.

and how I do to run the code: CTRL + a then shift + enter

So I want to know how to run all the lines at once

Please note that in an OCaml source file, there is no need for ;; to separate top-level definitions.

let x = 4
let y = 5
let z = 8

Works just as well as:

let x = 4;;
let y = 5;;
let z = 8;;

The ;; is primarily used within REPLs like utop to indicate the end of an expression, but should never be necessary in an OCaml source file.

If you remove those ;; tokens, and Ctrl-A, Shift-Enter, you will see the following in your VSCode Terminal output.

# let x = 3
  let y = 5
  let z = 2
  let t = 5
  ;;
val x : int = 3
val y : int = 5
val z : int = 2
val t : int = 5
#