The plan

There are several methods that are commonly used to determine sources of errors:

• Verbose inline messages: Obliterate your code with if statements and attempt to detect various errors.

• assert(...). In C and C++, you can use the assert(...) macro to halt your program if the specified condition is not met. A valid use of assert(...) might be
  assert(x==5);

• Use a debugger to step through your code.

• Use a memory profiler to detect bad uses of heap memory.

• Use a ``Instrumentation system'', ie. Valgrind to detect various errors.