Another C question tonight

This is a discussion on Another C question tonight within the C Programming forums, part of the General Programming Boards category; I want to write a function that simulates an ATM operation. If a user incorrectly enters their pin more than ...

  1. #1
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    Another C question tonight

    I want to write a function that simulates an ATM operation.

    If a user incorrectly enters their pin more than 3 times, I want to show an error.

    This program is simple, so the only way the user can incorrectly enter a pin is if they enter less than four digits.

    How would I write this function?

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    What have you tried?
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

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    Basically What I'm doing ruling out entries that are less than 1000. It's not working. Maybe it's the way I link int getPin to the main.. I'm not sure

    Code:
    #include <stdlib.h>
    #include <stdio.h>
    #include <time.h>
    
    //Global Dec's
    int getPin ();
    void getReciept (void);
    void menuChoose (void);
    
    int main (void)
    {
        //Local Dec's
        int attempts;
      
            
        printf("Welcome to Virtual Bank at West/n");
        attempts = getPin ();
        if (attempts <= 3)
        {
        getReciept();
        menuChoose();
    }
        else
        system("pause");
        return 0;
    }
        
    //getPin
    
    int getPin ()
    {
        int pin;
        int attempts;
        printf("Please enter pin number: \n");
    
         if (scanf("%d", &pin) < 1000)
            {
            attempts++;
            printf("Please re-enter pin number: \n");
            if (attempts > 3)
            printf("Sorry you can't continue, contact your bank for assistance.");
            }
         else
         return attempts;
    }//end getPin

  4. #4
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    hint: scanf doesn't return the number that it scanned

  5. #5
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    I don't follow, sl4nted

  6. #6
    Just Lurking Dave_Sinkula's Avatar
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    And you need to loop with a loop of some sort. And you need to initialize uninitialized values before modifying/examining them.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  7. #7
    "I Win!" by U. Lose vart's Avatar
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    Quote Originally Posted by imfrrreal
    I don't follow, sl4nted
    you should read the decription of the scanf and make a special point on the return value of that function to use it properly
    To be or not to be == true

  8. #8
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    OMG I forgot to loop.

    Duhh

    Thank you!!!!

    I'll try fixing that and if I have another issue I'll post.

  9. #9
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    Code:
    if (scanf("%d", &pin) < 1000)
    I assume your test to see if its less than 3 digits here.

    try this

    add another variable int ret; it will hold scanfs return
    so
    ret = scanf("%d", &pin);
    printf("Returned: %d\n", ret);

    should show you whats going wrong

  10. #10
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    Ok, check out int getPin now.. It's still not working properly.. after 2 attempts it moves on to getReciept in main.



    Code:
    #include <stdlib.h>
    #include <stdio.h>
    #include <time.h>
    
    //Global Dec's
    int getPin ();
    void getReciept (void);
    void menuChoose (void);
    
    int main (void)
    {
        //Local Dec's
        int attempts;
      
            
        printf("Welcome to Virtual Bank at West\n");
        attempts = getPin ();
        if (attempts < 3)
        {
        getReciept();
        menuChoose();
    }
        else
        system("pause");
        return 0;
    }
        
    //getPin
    
    int getPin ()
    {
        int pin;
        int attempts = 0;
        printf("Please enter pin number: \n");
        scanf("%d", &pin);
         while (pin < 1000)
            {
            attempts++;
              
            if (attempts < 3)
            {
            printf("Please re-enter your pin: \n");
            scanf("%d", &pin);
            } 
            else
            {
            printf("Sorry you can't continue, contact your bank for assistance.");
            return attempts;
             }
            system("pause");
            return attempts;
            }
    }//end getPin

  11. #11
    "I Win!" by U. Lose vart's Avatar
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    you problem is indentation - fix it and you will see the problem with the getPin function (when and what it returns...
    For example what it will return when 1001 is entered
    To be or not to be == true

  12. #12
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    nevermind
    Last edited by imfrrreal; 12-12-2006 at 01:36 AM.

  13. #13
    Chi! whiteflags's Avatar
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    I prefer to do error checking with a string myself. That way, input errors are independent of and easier to find than problems with scanf or magic numbers.

    Here's something that would work. I doubt it's bulletproof, and it should help you nonetheless:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int getPin ( int *somepin )
    {
       char pinstr[6]; /* Just big enough I think */
       if ( fgets(pinstr, sizeof pinstr, stdin) != NULL )
       {
          char *tail = pinstr;
          while ( isdigit(*tail) )
          {
             tail++;
          }
    
          if ( tail - pinstr == 4 /* checking length */ && (*tail == '\0' || *tail == '\n') )
          {
             *somepin = atoi(pinstr);
             return 1; /* success!! */
          }
       }
    
       return 0; /* failure :( */
    }
    
    int main ( void )
    {
       int mypin, attempts = 0;
       while ( attempts < 3 )
       {
          printf("Enter PIN: ");
          fflush(stdout);
          if ( getPin(&mypin) )
          {
             attempts++;
          }
          else
          {
             printf("Not a valid entry.\n");
          }
       }
    
       return 0;
    }
    
    /* output:
    Enter PIN: q123
    Not a valid entry.
    Enter PIN:   12
    Not a valid entry.
    Enter PIN: aswd
    Not a valid entry.
    Enter PIN: 1234
    Enter PIN: 1234
    Enter PIN: 1001
    */
    It doesn't have to be difficult.

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