CameraSwitch

using Cinemachine;

public class CameraSwitch : MonoBehaviour
{
    public enum CameraType
    {
        None =-1,
        Main,
        First,
        Third,
        Back
    }

    [Header ( "Cinemachine Virtual Cameras" )]
    public CinemachineVirtualCamera MainVirtualCamera;
    public CinemachineVirtualCamera FirstVirtualCamera;
    public CinemachineVirtualCamera ThirdVirtualCamera;
    public CinemachineVirtualCamera BackVirtualCamera;

    private CinemachineVirtualCamera[] virtualCameras;
    public CameraType CurrentCameraType { get; private set; }


    private void Start ( )
    {
        virtualCameras = new CinemachineVirtualCamera [ ] { MainVirtualCamera, FirstVirtualCamera, ThirdVirtualCamera, BackVirtualCamera };
        ChangeCamera ( CameraType.Main );
    }


    public void ChangeCamera ( CameraType cameraType )
    {
        for ( int i = 0; i < virtualCameras.Length; i++ )
            virtualCameras [ i ].gameObject.SetActive ( false );
        if ( cameraType != CameraType.None )
                virtualCameras [ ( int ) cameraType ].gameObject.SetActive ( true );
        CurrentCameraType = cameraType;
    }


    private void Update ( )
    {
        if ( Input.GetKeyDown ( "t" ) )
            if ( CurrentCameraType == CameraType.First )
                ChangeCamera ( CameraType.Main );
            else
                ChangeCamera ( CameraType.First );

        if ( Input.GetKeyDown ( "b" ) )
            ChangeCamera ( CameraType.Back );

        // Don't know how you wanted your third camera activated. But your logic would go here...
    }
}