As we continue our timer journey...

Better output

Up to this point in your journeyings of the wonderful world of C++ you have been using cout to do output. This is soooooo boring. WIBNIF we could make a 7-segment timer display? Lets try.

A 7-segment display looks like the following:

But before we can get an oject of type 7-segment display we need to first define a segment object. And not only do we need to define it, but we must make it general enough so that we could use it in many applications.

Lets look at a header file for our segement called segment.h

• The construct

      #ifndef SEGMENT_H_
      #define SEGMENT_H_
      decl of class segment
      #endif

  makes it so that even if segment.h is included multiple times, the class is only declared just once.
• segment.h only contains the class declaration. Essentially this is all that you need to use the class.
• The member functions defintions are elsewhere.
• The private data for the class segment is where, on. This basically means that a segment knows where it is and knows if it is on or off. Nothing else.

Lets examine the file segment.cpp

• We get the class segment declaration via:

  	#include "segment.h"

• Contained in segment.cpp are the member function definitions for a segment object.
• We change the display only when the on/off stage changes for a segment.

And how about a demo of our segment segmentTest.cpp

• This is a simple driver program to test and see if the segment class has been defined correctly and is in working condition.
• It is always a good idea to write a simple driver to check out a class before using it in something that is complicated.

Now lets design another class sevenSegDisplay which is in the file 7seg.h

• This file contains the class declaration for a sevenSegDisplay.
• We again use the #ifndef, #define, #endif construct.
• The member functions are constructors, clear, and show.
• The private data are color, objects for each of the seven segments.
• Notice that we included this line:

  #include "segment.h"

  This ensures that the segment class is known to the compiler.

Now lets look at 7seg.cpp

• Notice the lines:

  #include "7seg.h"
  #include "segment.h"

  The latter isn't necessary since 7seg.h includes it anyway. So why do it? It is good programming style to include everything you explicitly reference.
• The constructor relies on default do-nothing constructor for segment.
• The member functions are clear and show.
• The show function looks big, but it is really just a large case statement that enumerates for each digit all the segments that have to be lit up. If you go through it carefully you will find that although long, it is quite simple.

Make sure you check out the driver 7segTest.cpp

Now lets make a class for a counter in file counterDisp.h

• Notice the statement

  #include "7seg.h"

• We have numerous constructors which gives us lots of flexibility.
• The private data is two sevenSegDisplays plus limits and the current value. This makes 2 * 7 = 14 segments all together. So we start to see the power we have by being able to manipulate 14 segments and have them work independently of each other.

Now lets examine a test run of our new counter

• Notice the includes

  #include "7seg.h"
  #include "counterDisp.h"

• The geometry used gives the outer boundaries and is depicted below:
• This geometry is good for knowing how this counter fits into the outside world.
• Which is nice because we can just ask for sevenSegDisplay by boundary in the constructor.
• The constants for the geometry are fractions so they are easy to change.
• Also note that show() always shows both digits.

See Demo counterDispTest.cpp

Now let's look at HMStimer.h

• Private member data includes 3 counters, which gives 3 * 2 * 7 = 42 segments.
• Also upper and lower limits for hours.
• Here we have a private member function showColon().
  • Needed only by other member functions.
  • Never called by any function outside the timer class.

And we run HMStimer.cpp

The geometry involved in the timer is given below:

• Notice that showColon() is called only in constructor, since it is never erased.
• Notice also the other member functions: ++, set(), and show().

See Demo HMSTimerTest.cpp for test run of timer.

A few notes about Assignment #10

• Add an alarm feature.
• Handout mentions two things you will have to do.