What is the easiest way to make a C++ program crash?

Try:

raise(SIGSEGV);  // simulates a standard crash when access invalid memory
                 // ie anything that can go wrong with pointers.

Found in:

#include <signal.h>

The abort() function is probably your best bet. It's part of the C standard library, and is defined as "causing abnormal program termination" (e.g, a fatal error or crash).