/in/foo.c: In function 'main':
/in/foo.c:5:8: error: 'n' undeclared (first use in this function)
 char a[n];
        ^
/in/foo.c:5:8: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:20:1: error: expected declaration or statement at end of input
 }
 ^
/in/foo.c:5:6: warning: unused variable 'a' [-Wunused-variable]
 char a[n];
      ^