/in/foo.cc: In function 'int main()':
/in/foo.cc:14:7: error: 'n' was not declared in this scope
  cin>>n:
       ^
/in/foo.cc:8:7: warning: unused variable 'a1' [-Wunused-variable]
  char a1[50001],b1[50001];
       ^
/in/foo.cc:8:17: warning: unused variable 'b1' [-Wunused-variable]
  char a1[50001],b1[50001];
                 ^
/in/foo.cc:10:6: warning: unused variable 'lena' [-Wunused-variable]
  int lena,lenb,lenc,x;
      ^
/in/foo.cc:10:11: warning: unused variable 'lenb' [-Wunused-variable]
  int lena,lenb,lenc,x;
           ^
/in/foo.cc:10:16: warning: unused variable 'lenc' [-Wunused-variable]
  int lena,lenb,lenc,x;
                ^
/in/foo.cc:10:21: warning: unused variable 'x' [-Wunused-variable]
  int lena,lenb,lenc,x;
                     ^