Why do these errors keep showing up with C#? Im a beginner with coding

using UnityEngine; using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

 public float movementspeed = 5.0f; 
 public float MouseSensitivity = 5.0f;
 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () {
     //Movement with mouse
     transform.Rotate(0.0f ,rotleftright,0.0f);
     float rotleftright = Input.GetAxis ("Mouse")*MouseSensitivity;

     // This is all movement coding
 float ForwardSpeed = Input.GetAxis("Vertical")* movementspeed;
 float sidespeed = Input.GetAxis("Horizontal")* movementspeed;
     Vector3 speed = new Vector3 (ForwardSpeed, 0.0f, sidespeed);
 CharacterController cc = GetComponent<CharacterController>();

     speed = transform.rotation * speed;

     cc.SimpleMove( speed );
 }

}

These errors pop up -Assets/Scripts/NewBehaviourScript.cs(16,40): error CS0841: A local variable rotleftright' cannot be used before it is declared -Assets/Scripts/NewBehaviourScript.cs(16,27): error CS1502: The best overloaded method match for UnityEngine.Transform.Rotate(float, float, float)' has some invalid arguments

-Assets/Scripts/NewBehaviourScript.cs(16,27): error CS1503: Argument #2' cannot convert object' expression to type `float'

Could someone please help me understand the problems in basic terms thank you :)