Good single character option function

This is a discussion on Good single character option function within the C Programming forums, part of the General Programming Boards category; Hi, I want to have the following in my program: "Encrypt message ? (Y / N):" If the user enters ...

  1. #1
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    Good single character option function

    Hi,

    I want to have the following in my program:

    "Encrypt message ? (Y / N):"

    If the user enters Y then a boolean variable is set to true and if they enter N a boolean variable is set to false.

    Any other character should result in the message above being displayed again.

    I've tried a number of different methods such as using getchar() and fgets(), but I can't find an elegant solution.

    Does anyone have any ideas?

    Thanks.

  2. #2
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    Code:
    do
    {
       displaymessage();
       char c;
       scanf("%c",&c);
    }while(!(c=='N' || c=='Y'));
    Code:
    >+++++++++[<++++++++>-]<.>+++++++[<++++>-]<+.+++++++..+++.[-]>++++++++[<++++>-] <.>+++++++++++[<++++++++>-]<-.--------.+++.------.--------.[-]>++++++++[<++++>- ]<+.[-]++++++++++.

  3. #3
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    Is there a way to achieve the same thing without using scanf?

  4. #4
    C++ Witch laserlight's Avatar
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    You could use getchar() too, I suppose.
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  5. #5
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    char key;

    Code:
    do
    {
       printf("Encrypt (Y / N)");
       key = getchar();
    
    }while(!(key=='N' || key=='Y'));
    results in the message being printed loads of times when you enter anything other than 'Y' or 'N'

  6. #6
    C++ Witch laserlight's Avatar
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    results in the message being printed loads of times when you enter anything other than 'Y' or 'N'
    You need to discard the newline left in the buffer with an extra getchar(), e.g.,
    Code:
    do
    {
        printf("Encrypt (Y / N)");
        key = getchar();
        getchar();
    } while (!(key == 'N' || key == 'Y'));
    Note that getchar() returns an int, not a char, though in this case it probably does not matter.

    EDIT:
    Actually, you should do more than discard the newline left in the buffer. You should discard all that is left in the buffer. For an example of how to do that, read How do I flush the input buffer?
    Last edited by laserlight; 03-15-2008 at 02:23 PM.
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  7. #7
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    I've tried this:

    Code:
    do
    {
        printf("Encrypt (Y / N)");
        while ((key = getchar()) != '\n' && key != EOF);
        getchar();
    } while (!(key == 'N' || key == 'Y'));
    But it doesn't seem to work.

    Any ideas?

    Thanks.

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    Do you mean to have an infinite, if empty, while loop? Edit: sorry, thought that the getchar below was in the loop -- just never mind.
    Last edited by tabstop; 03-15-2008 at 05:25 PM.

  9. #9
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    I'd reccomend using:
    Code:
    char key[2]={0};
    do{
      displaymessage();
      scanf("&#37;1s",key);
    }while(key[0]!='N' || key[0] != 'Y');
    That'll take care of the pesky whitespace characters in the buffer. However, that'll still act weird if the user enters a word like "ORANGE", instead of a single character. It will read in the and discard characters up to the 'N', displaying the message 4 times (3 times after ORANGE is typed). Then it will proceed to the next instruction with "GE" still in the buffer.
    It is too clear and so it is hard to see.
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  10. #10
    Internet Superhero
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    How "doesn't it seem to work", be more specific.

    key is a char? right? Why are you comparing it in your loop with EOF?

    Code:
    do
    {
        printf("Encrypt (Y / N)");
        while ((key = getchar()) != '\n' && key != EOF);
        getchar();
    } while (!(key == 'N' || key == 'Y'));

    This getchar(); call is not needed, unless you want your user to press enter twice after inputting the number ofcourse?
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  11. #11
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    Quote Originally Posted by Neo1 View Post
    How "doesn't it seem to work", be more specific.

    key is a char? right? Why are you comparing it in your loop with EOF?

    Code:
    do
    {
        printf("Encrypt (Y / N)");
        while ((key = getchar()) != '\n' && key != EOF);
        getchar();
    } while (!(key == 'N' || key == 'Y'));

    This getchar(); call is not needed, unless you want your user to press enter twice after inputting the number ofcourse?
    Sorry, that getchar() was meant to be removed. It actually looks like:

    Code:
    do
    {
        printf("Encrypt (Y / N)");
        while ((key = getchar()) != '\n' && key != EOF);
       
    } while (!(key == 'N' || key == 'Y'));

  12. #12
    Dr Dipshi++ mike_g's Avatar
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    eponymous: You are flushing the input buffer but not getting a character for key now. I imagine you want something like this instead:
    Code:
    do
    {
        printf("Encrypt (Y / N)");
        while ((key = getchar()) != '\n' && key != EOF);
        key = getchar();
    } while (!(key == 'N' || key == 'Y'));
    It may also be a good idea to convert to uppercase too.

  13. #13
    and the hat of sweating
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    If your compiler/platform supports the <conio.h> header, why not just use getch() or getche()? There's other solutions listed in the FAQ section.

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