Why pressing the up and down key doesn't mean the body in correct forward and back direction?

using UnityEngine;
using System.Collections;

public class CameraMotor : MonoBehaviour {
    CharacterController c;
    float rotateSpeed;
    // Use this for initialization
    void Start () {
        c = GetComponent<CharacterController>();
        rotateSpeed = 3.0f;

    }
	
	// Update is called once per frame
	void Update () {
        if(Input.GetKey(KeyCode.LeftArrow))
        {
            transform.Rotate(0, Input.GetAxis("Horizontal") * rotateSpeed, 0);
        }
        else
            if (Input.GetKey(KeyCode.RightArrow))
        {
            transform.Rotate(0, -Input.GetAxis("Horizontal") * rotateSpeed, 0);
        }
        else
            if (Input.GetKeyDown(KeyCode.UpArrow))
        {
            c.Move(Vector3.forward);
        }
        else
            if (Input.GetKeyDown(KeyCode.DownArrow))
        {
            c.Move(Vector3.back);
        }

    }
}

using UnityEngine;
using System.Collections;

 public class CameraMotor : MonoBehaviour {
     CharacterController c;
     float rotateSpeed;
     // Use this for initialization
     void Start () {
         c = GetComponent<CharacterController>();
         rotateSpeed = 3.0f;
 
     }
     
     // Update is called once per frame
     void Update () {
         if(Input.GetKey(KeyCode.LeftArrow))
         {
             transform.Rotate(0, Input.GetAxis("Horizontal") * rotateSpeed, 0);
         }
         else
             if (Input.GetKey(KeyCode.RightArrow))
         {
             transform.Rotate(0, -Input.GetAxis("Horizontal") * rotateSpeed, 0);
         }
         else
             if (Input.GetKeyDown(KeyCode.UpArrow))
         {
             c.Move = new Vector3(Vector3.forward);
         }
         else
             if (Input.GetKeyDown(KeyCode.DownArrow))
         {
             c.Move = new Vector3(Vector3.back);
         }
 
     }
 }

Try this, you have to declare the position as a new vector3. (I’m not sure if this will work I’m not somewhere I can check for sure)