/in/foo.cc: In constructor 'BigNum::BigNum()':
/in/foo.cc:18:43: error: 'memset' was not declared in this scope
     BigNum(){ len = 1;memset(a,0,sizeof(a)); }   //构造函数
                                           ^
/in/foo.cc: In constructor 'BigNum::BigNum(int)':
/in/foo.cc:44:25: error: 'memset' was not declared in this scope
     memset(a,0,sizeof(a));
                         ^
/in/foo.cc: In constructor 'BigNum::BigNum(const char*)':
/in/foo.cc:56:25: error: 'memset' was not declared in this scope
     memset(a,0,sizeof(a));
                         ^
/in/foo.cc:57:15: error: 'strlen' was not declared in this scope
     l=strlen(s);   
               ^
/in/foo.cc: In copy constructor 'BigNum::BigNum(const BigNum&)':
/in/foo.cc:76:25: error: 'memset' was not declared in this scope
     memset(a,0,sizeof(a)); 
                         ^
/in/foo.cc: In member function 'BigNum& BigNum::operator=(const BigNum&)':
/in/foo.cc:84:25: error: 'memset' was not declared in this scope
     memset(a,0,sizeof(a)); 
                         ^
/in/foo.cc: In function 'std::istream& operator>>(std::istream&, BigNum&)':
/in/foo.cc:94:20: error: 'strlen' was not declared in this scope
     int l=strlen(ch);
                    ^