selection problem

This is a discussion on selection problem within the C Programming forums, part of the General Programming Boards category; Hello guys, i have this small problem. when i run this code and select 1(new user) it should just print ...

  1. #1
    Registered User
    Join Date
    May 2007
    Posts
    12

    selection problem

    Hello guys, i have this small problem. when i run this code and select 1(new user) it should just print out Testing 1 only but it print out another Invalid Selection. What is the problem here??

    Lot of help, Thanks

    Coding
    Code:
    int main()
    {
    	int select = 0;
            while (select != 51)
            {
                    printf("1. New User\n");
                    printf("2. Existing User\n");
                    printf("3. Exit\n");
                    printf("Please Enter Selection [ 1-3 ] : ");
                    select = getchar();
    
                    switch (select)
                    {
                            case 49: printf("Testing 1\n");
    				 break;
    
                            case 50: printf("Testing 2\n");
                                     break;
    
                            case 51: printf("Good Bye\n");
    				 break;
    
                            default: printf("Invalid Selection\n");
                                     break;
                    }
            }
    }
    Result
    Please Enter Selection [ 1-3 ] : 1
    Testing 1
    1. New User
    2. Existing User
    3. Exit
    Please Enter Selection [ 1-3 ] : Invalid Selection
    1. New User
    2. Existing User
    3. Exit
    Please Enter Selection [ 1-3 ] : 2
    Testing 2
    1. New User
    2. Existing User
    3. Exit
    Please Enter Selection [ 1-3 ] : Invalid Selection
    1. New User
    2. Existing User
    3. Exit
    Please Enter Selection [ 1-3 ] : 3
    Good Bye

  2. #2
    Deathray Engineer MacGyver's Avatar
    Join Date
    Mar 2007
    Posts
    3,211
    This is where knowing how things happen under the hood, so to speak, help with understanding how to write proper code.

    Let's take a look at what you're doing:

    The program first prompts you for a value. The input buffer is empty. You didn't enter anything, yet, so it asks you for a value. You enter '1' and then press Enter. Here's what the input buffer looks like now:

    Code:
    '1', '\n'
    getchar() grabs the first char you typed, which is the '1', and that's why it prints "Testing 1". Now it loops and it tries to read another selection. The input buffer looks like this:

    Code:
    '\n'
    So getchar() doesn't ask you for another character. It's already got one in the buffer. So it selects the '\n'.

    This is why you have "Invalid Selection", because it's reading the '\n' as your input.

    You repeat the same things with 2 and 3 later on.

    A hackish solution is to just perform a double getchar(). The problem with that is if you have a dumb user that wishes to type a book. Consider if the user enters this:

    Code:
    "It was the best of times and the worst of times..."
    The buffer starts out looking like this:

    Code:
    'I', t', ' ', 'w', 'a', 's'....
    This is obviously going to cycle for awhile telling the user they entered invalid entries.

    So what you could do is have an extra int called c. Call getchar() to read the user's first value like you normally do, and then run this line:

    Code:
    while(((c = getchar()) != '\n') && (c != EOF));
    This will keep reading from the input buffer until either '\n' or EOF is reached and get the input lined up for the next entry.

  3. #3
    int x = *((int *) NULL); Cactus_Hugger's Avatar
    Join Date
    Jul 2003
    Location
    Banks of the River Styx
    Posts
    902
    getchar() reads a single char. First, it reads a '1', and your program processes it. On the next iteration, it sees the '\n' (newline) that you typed after the 1.

    scanf() might serve you better here, or you'll need to wrap getchar() with something so more intelligence.
    Also, instead of case 49, use case '1' - just incase '1' != 49, and it self-documents to boot.
    long time; /* know C? */
    Unprecedented performance: Nothing ever ran this slow before.
    Any sufficiently advanced bug is indistinguishable from a feature.
    Real Programmers confuse Halloween and Christmas, because dec 25 == oct 31.
    The best way to accelerate an IBM is at 9.8 m/s/s.
    recursion (re - cur' - zhun) n. 1. (see recursion)

  4. #4
    Registered User
    Join Date
    May 2007
    Posts
    12

    Smile

    Thanks a lot guys =)

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Laptop Problem
    By Boomba in forum Tech Board
    Replies: 1
    Last Post: 03-07-2006, 06:24 PM
  2. Replies: 5
    Last Post: 11-07-2005, 11:34 PM
  3. searching problem
    By DaMenge in forum C Programming
    Replies: 9
    Last Post: 09-12-2005, 02:04 AM
  4. half ADT (nested struct) problem...
    By CyC|OpS in forum C Programming
    Replies: 1
    Last Post: 10-26-2002, 09:37 AM
  5. Replies: 0
    Last Post: 02-05-2002, 07:44 PM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21