AWK: how to match a comma - regex

Question

I want to return lines from awk with a pattern "C," or ".,C" or ".,C,.*".
For example:
Valid
C,G
G,C
G,C,A
Invalid
G,CC
My code is below:
echo G,CC | awk '$0 ~ /^C,+.*|.*,C,*.*/ {print $0}'
output:
G,CC
I hope it returns nothing to me. Unfortunately, it returns "G,CC" to me.
How do I solve this problem?
Edit:
Based on the answers from #Emma and #perreal. I used a shorter command line to solve my question:
awk '$0 ~ /^C,.*|.*,C,.*|.*,C$/ {print $0}'
Until now, it works well. Thanks for your help!!

Answer 1

Could you please try following.
awk '!/CC/ && /^C,+.*|.*,C,*.*/' Input_file

Answer 2

The + is not necessary in ^C,+.*, since you already match the comma and also match whatever comes after.
The * right after the second comma is not correct in .*,C,*.*. It makes the comma optional so it can also match G,CC (.*, matches G, and C,* matches CC).
This should work:
awk '$0 ~ /^[GCA](,[GCA])*$/ && /C/ {print $0}'

Answer 3

My guess is that maybe this would also work:
awk '$0 ~ /^([A-Z],C,[A-Z]|[A-Z],C|C,[A-Z])$/ {print $0}'
Demo
Advice
Mr. Rankin is advising that:
It is equivalent to awk '/^([A-Z],C,[A-Z]|[A-Z],C|C,[A-Z])$/'. Output
with print is the default operation along with the match against the
record.

Answer 4

$ awk '/(^|,)C(,|$)/' file
C,G
G,C
G,C,A

Answer 5

More alternatives
In other words, you want to select lines with "C" as word? If yes, here are 2 solutions:
grep -w C
grep -E '\<C\>'
The first one advises grep to match only whole words. The second line uses begin-word and end-word patterns. These pattern can be used with awk too:
awk '/\<C\>/ {print}'
A complete different solution (and different form other answers too) is to add commas at both ends before comparing ,C,:
awk '"," $0 "," ~ /,C,/ {print}