// define_debug.cc
// for g++ compiled with: 
// g++ -DDEBUG -o define_debug define_debug.cc
// -DDEBUG is equivalent to the source #define DEBUG
// If we recompile without -DDEBUG then the debug test 
// below will not run
#include <iostream>
using namespace std;

int main() {
  #ifdef DEBUG
  cout << "I'm doing a debug test now." << endl;
  #endif
  cout << "Hello, world" << endl;
}