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Homework Help: Using Enumerators

  1. Mar 13, 2010 #1
    I'm working on a project for my microcontrollers course. It involves programming a pathfinding robot that uses 5 reflected light sensors to follow a track. Since the code that we were provided that was written I don't know how long ago fails as hard as it does I decided to re-write the whole control system.

    Only thing is to simplify things when programming the logic into this thing I want to use enums to control the speed of each motor.

    I have NO clue how this guy put the code together, but it's just a big partially commented mess.

    Here is the applicable code from the header file
    Code (Text):

    enum motor_speed_setting { rev_fast, rev_medium, rev_slow, stop, slow, medium, fast };

    enum motor_selection { left, right };

    void set_motor_speed(enum motor_selection the_motor, enum motor_speed_setting motor_speed, int speed_modifier);
    and here is the code from the source file

    Code (Text):

    void set_motor_speed(enum motor_selection the_motor, enum motor_speed_setting motor_speed, int speed_modifier)


        const static int motor_speeds[] = { -800, -600, -400, 0, 400, 600, 800};

        int duty_cycle;

        enum e_direction {reverse,forward} dir_modifier= forward;
    Now what I want to do is have my array (or vector, I like them better) with similar values, with enumerated values for each setting. I just don't get how this stuff goes together.

    How do I go about enumerating values to the values in the array/vector? I know how to assign them when creating the array by making the values equal something, but this fellow seemed to create the values, then enumerate them.
    Last edited: Mar 13, 2010
  2. jcsd
  3. Mar 13, 2010 #2


    Staff: Mentor

    You're making this much more complicated than it really is. An enum (short for enumeration or enumerated type) is nothing more than a type that lists a bunch of named constants. A variable of this type can be one of the values in the enumeration. That's all.

    You don't enumerate anything; you just use those named constants. Do a search for C++ enum and you'll find lots of pages that describe enumerated types. Here's one that I found: http://www.cppreference.com/wiki/keywords/enum.

    Your set_motor function takes three arguments: the first is the_motor, the second is a motor speed, and the third is a speed modifier. A call to this function would look like this:

    set_motor( left, rev_medium, 2);

    This call would apparently set the motor speed to medium for the left motor (the motor in the left wheel?). I don't know what the 2 would do, since you don't show enough of the code for me to be able to tell.
  4. Mar 13, 2010 #3
    I didn't code that, it was provided. The massive confusion I had when I tried to figure out what was going on is the reason I'm re-writing everything. I did manage to figure it out with that though. Thanks for the help.
  5. Mar 13, 2010 #4


    Staff: Mentor

    Right, I knew that you didn't code it. The thing about using enums is that the named constants give you a better idea of what's going on than just constants would.

    For example, a call to set_motor( 1, 3, 2); would be much harder to figure out.
  6. Mar 13, 2010 #5
    That makes sense.
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