The error you have noticed is simple: You forgot the semicolon at the end of this line:
char goAgain='y'
Adding it will fix the compilation problem:
char goAgain='y';
But...then you have more problems.
1) You don't read the choice from the user.
2) You break out of the switch regardless of the user selection of "y" or "n".
3) Your condition doesn't check the user PIN is 1234, it assigns it. "=" is assignment, "==" is comparison.
4) You should be using your "goAgain" variable in the loop termination condition.