public class soundcontrol : MonoBehaviour {
    AudioSource theaudio ;
    public AudioClip clip1;
    public AudioClip clip2;
    public AudioClip clip3;
    AudioClip[] cliparray;
    int currentclip = -1;
    int maxclip = 0;
    bool isclip1null = false;
    bool isclip2null = false;
    bool isclip3null = false;

    // Use this for initialization
    void Start () {
    }

    // Update is called once per frame
    void Update () {
        maxclip = 0;
        if (clip1 != null) {
            isclip1null = true;
            cliparray [maxclip] = clip1;
            maxclip = maxclip + 1;
        }
        if (clip2 != null) {
            isclip2null = true;
            cliparray [maxclip] = clip2;
            maxclip = maxclip + 1;
        }
        if (clip3 != null) {
            isclip3null = true;
            cliparray [maxclip] = clip3;
            maxclip = maxclip + 1;
        }
        if (!theaudio.isPlaying) { // the error is here
            if (!((maxclip - 1) == -1)) {
                currentclip = currentclip + 1;
                if (currentclip > maxclip) {
                    currentclip = 0;
                }
                if (!((maxclip - 1) == -1)) {
                    theaudio.PlayOneShot (cliparray [currentclip]);
                }
            }
        }
        if ((maxclip - 1) == -1) {
            Debug.Log (" no clip attached ");
        }
    }
}

// When the audio component has stopped playing, play otherClip
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public AudioClip otherClip;
    AudioSource audio;

    void Start() {
      audio = GetComponent<AudioSource>();
    }

    void Update() {
        if (!audio.isPlaying) {
            audio.clip = otherClip;
            audio.Play();
        }
    }
}