View Compilation Error

0_0_34448166_28100.cpp: In function 'int main()':
0_0_34448166_28100.cpp:7:5: error: 'cin' was not declared in this scope
     cin>>n;
     ^
0_0_34448166_28100.cpp:14:21: error: 'cout' was not declared in this scope
             case'+':cout << a+b<< endl;break;
                     ^
0_0_34448166_28100.cpp:14:35: error: 'endl' was not declared in this scope
             case'+':cout << a+b<< endl;break;
                                   ^
0_0_34448166_28100.cpp:19:32: error: 'fixed' was not declared in this scope
                         cout <<fixed<<setprecision(2)<<a/(b*1.0)<< endl;//小数点后保留两位 
                                ^
0_0_34448166_28100.cpp:19:53: error: 'setprecision' was not declared in this scope
                         cout <<fixed<<setprecision(2)<<a/(b*1.0)<< endl;//小数点后保留两位 
                                                     ^