Adjusting Mouse Sensitivity through GUI.HorizontalSlider (c#)

I have here a character controller script where bothe the movement and camera rotation are in one script. Can anyone help me fix this please? Do i have to access the “publicfloat mousesensitivity = 5.0f;”? if so can anyone help me Thanks again! Also if possible can you guys provide the editted code as a whole kinda sorta still a noob sorry…

Controller script:

using UnityEngine;
using System.Collections;

public class Controller : MonoBehaviour {

	public float movementspeed = 5.0f;
	public float mousesensitivity = 5.0f;
	public float jumpspeed = 20.0f;

	float  verticalRotation = 0;
	public float updownrange = 60.0f;

	float VerticalVelocity = 0;

	// Use this for initialization
	void Start () {
		Screen.lockCursor = false;
	}
	
	// Update is called once per frame
		
		void Update () {
			CharacterController cc = GetComponent <CharacterController> (); 

	//Rotation
		float rotleftright = Input.GetAxis("Mouse X") * mousesensitivity;
			transform.Rotate (0, rotleftright, 0);

		verticalRotation -= Input.GetAxisRaw("Mouse Y") * mousesensitivity;
			verticalRotation = Mathf.Clamp (verticalRotation,-updownrange ,updownrange);
				Camera.main.transform.localRotation = Quaternion.Euler (verticalRotation, 0, 0);


	//Movement


		float forwardspeed = Input.GetAxis("Vertical") * movementspeed ;
		float sidespeed = Input.GetAxis("Horizontal") * movementspeed ;

		VerticalVelocity += Physics.gravity.y * Time.deltaTime;


		Vector3 speed = new Vector3 (sidespeed, VerticalVelocity , forwardspeed );

		speed = transform.rotation * speed;

	

		cc.Move ( speed * Time.deltaTime );
	}
}

Slider Script:

using UnityEngine;
   using System.Collections;

    public class HSlider : MonoBehaviour {
    float hSliderValue = 5.0f;
    // Use this for initialization
    void Start () {
 
    }
 
    // Update is called once per frame
    void Update () {
 
    }
    OnGUI {
        Rect slider = new Rect (50, 30, 100, 30);
        hSliderValue = GUI.HorizontalSlider(slider,hSliderValue,1.0f,100.0f);
    }
 
}

Hi, I solved the script, the only thing you have to do is to put the content of a OnGui inside a void, important not to do the OnGui void because it will fail, Here is the script solved:

using UnityEngine;
using System.Collections;

 public class HSlider : MonoBehaviour {
 float hSliderValue = 5.0f;
 // Use this for initialization
 void Start () {

 }

 // Update is called once per frame
 public void Update () {
     Rect slider = new Rect (50, 30, 100, 30);
     hSliderValue = GUI.HorizontalSlider(slider,hSliderValue,1.0f,100.0f);
 }

}