For example, int a;; ; Represents the statement "plastic variable a";
int a,b,c; There are three integer variables a, b and C.
But int a,; b; c; The computer will look at the first sentence like this: there is an integer variable A. The second sentence B. The third sentence C. "
Because B and C appear separately, the computer can't recognize what they are, so the computer has an error.
Then you can write it like this
int a;
int b;
int
Or int a;; ; int b; int c;
Then the computer can recognize it.
You just need to remember that commas are the separators of variables, and semicolons indicate the end of statements.