How To: Count To 16 Billion Billion

While it is not part of the C++ language, both the Microsoft.NET and GNU compilers support 64-bit integers. The unsigned versions of these can store numbers as large as 16,000,000,000,000,000,000 (or more exactly, 2⁶⁴-1).

32-bit ints only go to 2 billion. The unsigned int goes to 4 billion. Need to go higher? Microsoft's __int64 goes to 8 billion billion, and the unsigned version goes to 16 billion billion! Borland compilers use this, too. Try this:

 
  cout << sizeof(unsigned int) << endl; // should be 4 bytes
  cout << sizeof(unsigned __int64) << endl; // should be 8 bytes
  unsigned __int64 a = 16;
  for (int i = 0; i < 20; i++)
  {
    cout << a << endl; // tops out at 16 billion billion
    a *= 10;
  }

In GNU, it's "long long" and "unsigned long long":


  cout << sizeof(unsigned int) << endl; // should be 4 bytes
  cout << sizeof(unsigned long long) << endl; // should be 8 bytes
  unsigned long long a = 16;
  for (int i = 0; i < 20; i++)
  {
    cout << a << endl; // tops out at 16 billion billion
    a *= 10;
  }

If you want to write compiler independent code, use something like this:

 
  #ifdef __GNUC__
  #define ULONGINT unsigned long long
  #endif
 
  #ifdef _WIN32
  #define ULONGINT unsigned __int64
  #endif

  #ifdef __BORLANDC__
  #define ULONGINT unsigned __int64
  #endif

  cout << sizeof(ULONGINT) << endl; // should be 8 bytes
  ULONGINT a = 16;
  for (int i = 0; i < 20; i++)
  {
    cout << a << endl; // tops out at 16 billion billion
    a *= 10;
  }