To execute one source line of your program, click on the Step push
  button on the push-button view of the main window.  This debugging
  technique (called stepping) is one of the most commonly used.

  After the line executes, the source view is updated and the
  current-location pointer marks the line whose code will execute next.

  Note the following points about source lines and the stepping behavior:

   -  A source line can consist of one or more programming language
      elements, depending on the language and coding style used.

   -  When you click on the Step push button, the debugger executes one
      executable line and suspends execution at the start of the next
      executable line, by skipping over any intervening nonexecutable
      lines.

   -  Executable lines are those for which instructions were generated by
      the compiler (for example, lines with routine call or assignment
      statements).  Executable lines have a toggle button to their left
      in the source view.

   -  Examples of nonexecutable lines are comment lines or lines with
      variable declarations without value assignments.  Nonexecutable
      lines do not have a toggle button to their left in the source view.

  Keep in mind that if you optimized your code at compilation time, the
  source code displayed might not reflect the code that is actually
  executing.

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