/in/foo.cc:4:31: error: ISO C++ forbids declaration of 'qiduan' with no type [-fpermissive]
   qiduan(int s1, int s2,int s3)
                               ^
/in/foo.cc: In function 'int qiduan(int, int, int)':
/in/foo.cc:12:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^