Prior to the compiler upgrade in May 2009, we serviced C and C++ submissions using GCC 3.4.2. That version of GCC relies on the old MS VC++ 6 runtime library, which does not support the %lld and %llu specifiers for signed and unsigned long long types but allows the standard-incompliant %lf and %lg specifiers for floating-point types. The new GCC 4.4.0 comes with its own ISO C-conformant implementation of the printf function. Now you can use %lld and %llu with either C/C++ compiler, but %lf and %lg only work with MS VC++ 2008 Express. As a rule of thumb, you should always use the %f and %g specifiers instead for floating-point types.