Over 1C, a 4 card major is ALWAYS shown unless you have a game-forcing hand with a much better holding in diamonds.

Thus, you bypass a diamond suit if you have one or you ignore raising partner's clubs and instead show a major.

1C 1D practically denies a major

After 1C-1D opener re-bids 1 of a major ONLY with an unbalanced hand.

Opener's re-bid of 1NT may have one or two 4 card majors!

1C 1D 1H guarantees an unbalanced hand. At least 5 clubs and 4 hearts.

1C 1D 1NT may have 1 or 2 four card majors

1C 1D 1NT 2H responder has a game-forcing hand with much better diamonds (say 6 diamonds and 4 hearts).