View Compilation Error

0_0_28721186_25708.cpp: In function 'int main()':
0_0_28721186_25708.cpp:17:9: error: 'cin' was not declared in this scope
  while (cin >> t)
         ^
0_0_28721186_25708.cpp:29:21: error: 'strlen' was not declared in this scope
    int L = strlen(st);
                     ^
0_0_28721186_25708.cpp:55:4: error: 'cout' was not declared in this scope
    cout << sum << endl;
    ^
0_0_28721186_25708.cpp:55:19: error: 'endl' was not declared in this scope
    cout << sum << endl;
                   ^