View Compilation Error

0_0_20424066_11668.cpp: In function 'int main()':
0_0_20424066_11668.cpp:9:5: error: 'cin' was not declared in this scope
     cin >> ca;
     ^
0_0_20424066_11668.cpp:21:7: error: 'cout' was not declared in this scope
       cout << a[k] << endl;
       ^
0_0_20424066_11668.cpp:21:23: error: 'endl' was not declared in this scope
       cout << a[k] << endl;
                       ^