can anyone please help convert these lines in C#?

transform.eulerAngles.y = -player.transform.eulerAngles.y;
moveDirection = Vector3 (0, 0, 40.0f);
moveDirection = transform.TransformDirection (moveDirection);
moveDirection *= runspeed;
characterController.SimpleMove (moveDirection * Time.deltaTime);

Im getting 2 errors in doing so .

Error 1: Cannot implicitly convert type float' to UnityEngine.Vector3’.

Error 2: Expression denotes a type', where a variable’, value' or method group’ was expected

I’m not too experienced with unity yet but maybe try something like this:
transform.eulerAngles = new Vector3(transform.eulerAngles.x, -player.transform.eulerAngles.y, transform.eulerAngles.z);
As eulerAngles.y is return value only.
Also you forgot new in moveDirection = new Vector3(0, 0, 40.0f);
I assume runspeed is Vector3?