View Compilation Error

0_0_29487258_23807.cpp: In function 'int main()':
0_0_29487258_23807.cpp:4:8: error: 'cin' was not declared in this scope
  while(cin>>n&&n)
        ^
0_0_29487258_23807.cpp:6:3: error: 'string' was not declared in this scope
   string a[1100];
   ^
0_0_29487258_23807.cpp:10:9: error: 'a' was not declared in this scope
    cin>>a[i];
         ^
0_0_29487258_23807.cpp:16:8: error: 'a' was not declared in this scope
     if(a[i]==a[j])
        ^
0_0_29487258_23807.cpp:31:3: error: 'cout' was not declared in this scope
   cout<<a[dex]<<endl;
   ^
0_0_29487258_23807.cpp:31:9: error: 'a' was not declared in this scope
   cout<<a[dex]<<endl;
         ^
0_0_29487258_23807.cpp:31:17: error: 'endl' was not declared in this scope
   cout<<a[dex]<<endl;
                 ^