New Unity Dropdown Menu to Change Game Resolution

UI can be used to process functions that are public ex: public void NameOfFunction(){} as for setting up resolution with drop down what you will need is UI button/DropDown Menu

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class settingmenu : MonoBehaviour {
 
     public bool screenres;
     Resolution[] resolutions;
     public Dropdown dropdownMenu;
     //public Vector2 Res;
 
     // Use this for initialization
     void Start () {
         resolutions = Screen.resolutions;
         for (int i = 0; i < resolutions.Length; i++)
         {
             dropdownMenu.options[i].text = ResToString(resolutions[i]);
             dropdownMenu.value = i;
 
             dropdownMenu.onValueChanged.AddListener(delegate { Screen.SetResolution(resolutions[dropdownMenu.value].width, resolutions[dropdownMenu.value].height, true); });
         }
     }
     
     // Update is called once per frame
     void Update () {
         Screen.fullScreen = screenres;
         //Screen.SetResolution((int)Res.x, (int)Res.y, screenres);
     }
     public void Full()
     {
         screenres = !screenres;
     }
     string ResToString(Resolution res)
     {
         return res.width + " x " + res.height;
     }
 }