/in/foo.c:2:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'main':
/in/foo.c:4:8: error: 'n' undeclared (first use in this function)
  int a[n];
        ^
/in/foo.c:4:8: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:17: warning: variable 'n' set but not used [-Wunused-but-set-variable]
  int number,i,j,n;
                 ^
/in/foo.c:4:6: warning: unused variable 'a' [-Wunused-variable]
  int a[n];
      ^