istream::operator >>
istream& operator >>( char* psz );

istream& operator >>( unsigned char* pusz );

istream& operator >>( signed char* pssz );

istream& operator >>( char& rch );

istream& operator >>( unsigned char& ruch );

istream& operator >>( signed char& rsch );

istream& operator >>( short& s );

istream& operator >>( unsigned short& us );

istream& operator >>( int& n );

istream& operator >>( unsigned int& un );

istream& operator >>( long& l );

istream& operator >>( unsigned long& ul );

istream& operator >>( float& f );

istream& operator >>( double& d );

istream& operator >>( long double& ld ); (16-bit only)

istream& operator >>( streambuf* psb );

istream& operator >>( istream& (*fcn)(istream&) );

istream& operator >>( ios& (*fcn)(ios&) );

这些是本来>>支持的类型。
对于cin来说,如cin>>(int)a，而输入一字符串，则会使cin陷入错误状态，故在输入之前应该先检查if（isdigit（a））。