how to solve in this error "The name `CowboyRap' does not exist in the current context" .using below script

using UnityEngine; using System.Collections;

public class Audio_RanGen : MonoBehaviour {

 public AudioClip[] sound=new AudioClip[1]{CowboyRap};
 
 
 // Use this for initialization
 void Start ()
 {
     
 }
 
 // Update is called once per frame
 void Update () 
 {
  
 }
 
 
 
 void OnGUI()
 {
     
     if(GUI.Button(new Rect(100,200,200,50),"Random Number Genaration"))
     {
         
         
         for(int i=0;i<14;i++)
         {
             print ("hiiii");
             print(sound.Length);
             print(sound[0]);
             audio.clip=sound[Random.Range(0,sound.Length)];
             audio.Play();
             
         }
         
         
     }
     
     
     
 }

}