I keep getting this error on my project and i cant figure it out! please help!

error C2143: syntax error : missing ')' before 'constant'

the line is:

while (selection == ('a','b','c', 'd', 'e', 'f', 'g', 'h', 'i','A','B' 'C', 'D', 'E', 'F', 'G', 'H', 'I');

also i know there is an easier way to write that line out but im not sure how i can do it. im a beginner at this so can any of you pros edit this line for me!