What belongs in an educational tool to demonstrate the unwarranted assumptions people make in C/C++?

The order of evaluation of subexpressions, including

• the arguments of a function call and
• operands of operators (e.g., +, -, =, * , /), with the exception of:
  • the binary logical operators (&& and ||),
  • the ternary conditional operator (?:), and
  • the comma operator (,)

is Unspecified

For example

  int Hello()
  {
       return printf("Hello"); /* printf() returns the number of 
                                  characters successfully printed by it
                               */
  }

  int World()
  {
       return printf("World !");
  }

  int main()
  {

      int a = Hello() + World(); //might print Hello World! or World! Hello
      /**             ^
                      | 
                Functions can be called in either order
      **/
      return 0;
  }