Switch input where nothing is impossible

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

public class DumbInput : MonoBehaviour {
    public KeyCode[] keysToListenFor;
    List<KeyCode> keyCodesThisFrame = new List<KeyCode>();

    void Update () {
        keyCodesThisFrame.Clear();
        if( keysToListenFor.Length == 0 ) {
            keysToListenFor = Enum.GetValues(typeof(KeyCode)) as KeyCode[];
        }

        foreach( KeyCode key in keysToListenFor ) {
            if( Input.GetKeyDown(key) ) {
                keyCodesThisFrame.Add(key);
            }
        }

        foreach( var key in keyCodesThisFrame ) {
            switch( key ) {
                case KeyCode.A:
                    Debug.Log("A was hit!");
                    break;
                case KeyCode.B:
                    Debug.Log("B was hit!!");
                    break;
                case KeyCode.C:
                    Debug.Log("C was hit!!!");
                    break;
            }
        }

    }

}