How do I make my inventory find the first slot available?

I already tried to do this but when ever I pick up an item it takes it to only the second slot!

Inventory script: using UnityEngine; using System.Collections; using System.Collections.Generic;

public class Inventory : MonoBehaviour { private Rect windowRect = new Rect(300, 100, 400, 400); static public Dictionary inventorynamesDictionary = new Dictionary () { {0, string.Empty}, {1, string.Empty}, {2, string.Empty}, {3, string.Empty}, {4, string.Empty}, {5, string.Empty}, {6, string.Empty}, {7, string.Empty}, {8, string.Empty}, {9, string.Empty} }; public static bool FirstSlot = false; public static bool SecondSlot = false; public static bool ThirdSlot = false; public static bool FourthSlot = false; public static bool FifthSlot = false; public static bool SixthSlot = false;

 ItemClass itemObject = new ItemClass();

 void Start (){



 }

 void Update () {
 

 }

 void OnGUI() {
     if(Input.GetKey (KeyCode.Tab))
     windowRect = GUI.Window(0, windowRect, DoMyWindow, "Inventory");
 
 }
 void DoMyWindow(int windowID) {



                     GUILayout.BeginArea (new Rect (0, 50, 400, 400));

                     GUILayout.BeginHorizontal ();
                     if (GUILayout.Button (inventorynamesDictionary [0], GUILayout.Height (50))) {
         if(inventorynamesDictionary[0] == itemObject.cm9Item.name)
         {
             Debug.Log("Equpuiped weapon!!");
         }
             }
                     GUILayout.Button (inventorynamesDictionary [1], GUILayout.Height (50));
                     GUILayout.Button (inventorynamesDictionary [2], GUILayout.Height (50));
                     GUILayout.EndHorizontal ();

                     GUILayout.BeginHorizontal ();
                     GUILayout.Button (inventorynamesDictionary [3], GUILayout.Height (50));
                     GUILayout.Button (inventorynamesDictionary [4], GUILayout.Height (50));
                     GUILayout.Button (inventorynamesDictionary [5], GUILayout.Height (50));
                     GUILayout.EndHorizontal ();
 

                     GUILayout.EndArea ();


 }
 

}

PickUpgun script

using UnityEngine; using System.Collections; using System.Collections.Generic;

public class PickUpGun : MonoBehaviour { public GameObject Gun; public GameObject Gun1; public bool GotPistol; private Ray mouseRay; private RaycastHit rayHit;

 private Dictionary<int, string> lootDictionary = new Dictionary <int, string>()
 {{0, string.Empty},
     {1, string.Empty},
     {2, string.Empty},
     {3, string.Empty},
     {4, string.Empty},
     {5, string.Empty}
 };
 ItemClass itemObject = new ItemClass();

 public GameObject objectwithInventory;

 Inventory Inventory ;

 // Use this for initialization
 void Start () {
     lootDictionary [0] = itemObject.cm9Item.name;
     lootDictionary [1] = itemObject.breadItem.name;
     lootDictionary [2] = itemObject.painkillersItem.name;
     Inventory = objectwithInventory.GetComponent<Inventory>();
 }
 
 // Update is called once per frame
 void Update () {
     mouseRay = Camera.main.ScreenPointToRay (new Vector3 (Screen.width / 2, Screen.height / 2,0));
     if (Input.GetKeyDown (KeyCode.E)) 
     {
         Physics.Raycast(mouseRay, out rayHit);
         if(rayHit.collider.transform.tag == "cm9")
         {
             Destroy(Gun);
             GotPistol = true;
             if(GotPistol = true){
                 if(Inventory.FirstSlot = false){
                 Inventory.inventorynamesDictionary [0] = lootDictionary[0];
                 Inventory.FirstSlot = true;
                 Debug.Log ("First Slot is now full");
                 }
             
                 if(Inventory.FirstSlot = true)
                 {
                     Inventory.inventorynamesDictionary [1] = lootDictionary[0];
                     Inventory.SecondSlot = true;

                 }
             
         }
 }

} } }