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public class PlayerPrefsController : MonoBehaviour
{
    const string MASTER_VOLUME_KEY = "master volume";
    const string DIFFICULTY_KEY = "difficulty";

    const float MIN_VOLUME = 0f;
    const float MAX_VOLUME = 1f;

    public static void SetMasterVolume(float volume)
    {
        if (volume >= MIN_VOLUME && volume <= MAX_VOLUME)
        {
            Debug.Log("Master Volume Set To " + volume);
            PlayerPrefs.SetFloat(MASTER_VOLUME_KEY, volume);
        }
        else
        {
            Debug.LogError("Master volume is out of range");
        }
    }

    public static float GetMasterVolume()
    {
       return PlayerPrefs.GetFloat(MASTER_VOLUME_KEY);
    }
}