You need to include all necessary header files.

The following set of includes can be used for C and C++:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <math.h>
#include <limits.h>
#include <assert.h>

The following set of includes can be used for the mini C++ only:

#include <iostream>
#include <iomanip>

The following set of includes can be used for full C++ only:

#include <algorithm>
#include <iomanip>
#include <list>
#include <ostream>
#include <streambuf>
#include <bitset>
#include <ios>
#include <locale>
#include <queue>
#include <string>
#include <complex>
#include <map>
#include <set>
#include <typeinfo>
#include <deque>
#include <iostream>
#include <memory>
#include <sstream>
#include <exception>
#include <istream>
#include <new>
#include <stack>
#include <valarray>
#include <iterator>
#include <numeric>
#include <stdexcept>
#include <vector>
#include <functional>
#include <limits>

using namespace std;