foo.cc: In function 'int get_pos(const int*, int, int)':
foo.cc:20:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.cc: In function 'void P()':
foo.cc:47:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&num);
     ~~~~~^~~~~~~~~~~
foo.cc:50:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d",&data1[i]);
         ~~~~~^~~~~~~~~~~~~~~~
foo.cc:54:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d",&data2[i]);
         ~~~~~^~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务