NullReferenceException: Object Reference not set to an instance of an object

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

public class Inventory : MonoBehaviour {

	public int Pistol = 0;
	public int Assault_Rifle = 0;
	public int Marine = 0;
	public UnityEngine.UI.Text CPistol;
	public UnityEngine.UI.Text CAssault_Rifle;
	public UnityEngine.UI.Text CMarine;

	void Start (){
		CPistol = GetComponent<Text> ();
		CAssault_Rifle = GetComponent<Text> ();
		CMarine = GetComponent<Text> ();
	}

	void Update(){
		CPistol.text = Pistol.ToString ();
		CAssault_Rifle.text = Assault_Rifle.ToString ();
		CMarine.text = Marine.ToString ();
	

	}
}

How exactly am I supposed to fix this?

Try This

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

public class Inventory : MonoBehaviour 
{

	public int Pistol = 0;
	public int Assault_Rifle = 0;
	public int Marine = 0;
	public Text CPistol;
	public Text CAssault_Rifle;
	public Text CMarine;



	void Update()
	{
		CPistol.text = Pistol.ToString ();
		CAssault_Rifle.text = Assault_Rifle.ToString ();
		CMarine.text = Marine.ToString ();
	}
}

assign CPistol,CassaultRifle, and Cmarine in the inspector