After 1 club opening anything besides 1 diamond is non-forcing and shows fewer than 12 points.

 

All these bids should be alerted:

1C                   1H                               natural in hearts with fewer than 12 points

1C                   1S                                natural in spades with fewer than 12 points

1C                   1NT                             responder may have a diamond suit

 

1C                   2D                               shows 6+ diamonds with 6-9 points

Note, 2 diamonds over 1 club usually is pre-emptive.  It was felt the 6-9 point hand was a better use of this bid.

 

1C                   3D                               6+ diamonds, 10-11 points

 

Inverted minor responses:

1C                   2C                               5+ clubs, no 4 card major 10-11 points

1C                   3C                               5+ clubs, no 4 card major, 6-9 points

 

 

Responder has 10 to a bad 12 points:

1C                   1H

1N                   2D                               new minor forcing

2H                                                       opener has 3 hearts

Responder has fewer than 12 points