How to compare common variables of two files?

I have two csv files, a and b.

These two csv have a common variable 'c', and the other variables have different types and numbers.

'After creating a new variable aa in file a, if the value of variable c in both files is the same, fill aa with 0, otherwise fill with 1'

Can we make a conditional statement like this?

Creating a new variable is not difficult, but creating a condition to compare the values of two files is difficult.

Any help please?

thank you