Thread: Using the Fall Through Feature of a Switch statement

  1. #1
    Registered User
    Join Date
    Sep 2006

    Using the Fall Through Feature of a Switch statement

    Just wanted to share this little beautiful illustration of the "fall through" feature of a switch statement, and how it can be used. (and why you need the break statement after every case, if you don't want it)

    This is the way I remember it working.

    /* The Twelve Days of Christmas lyrics, showing the "fall through" feature of the switch statement 
    #include <stdio.h>
    int main(void) {
      int day;
      char numbers[][13]={"empty","first","second","third","fourth","fifth","sixth","seventh","eight","ninth","tenth","eleventh","twelfth"};
      printf("\n\n\n\t\t   Welcome to the Twelve Days of Christmas");
      for(day = 1; day < 13; day++) {
        printf("\n\n On the %s Day of Christmas, My True Love Gave to Me:\n", numbers[day]);
        switch(day) {
          case 12: printf("\n 12 Drummers Drumming");
          case 11: printf("\n 11 Pipers Piping");
          case 10: printf("\n 10 Lords a'Leaping");
          case 9: printf("\n  9 Ladies Dancing");
          case 8: printf("\n  8 Maids a'Milking");
          case 7: printf("\n  7 Swans a'Swimming");
          case 6: printf("\n  6 Geese a'Laying");
          case 5: printf("\n  5 Golden Rings");
          case 4: printf("\n  4 Calling Birds");
          case 3: printf("\n  3 French Hens");
          case 2: printf("\n  2 Turtle Doves");
          case 1: 
            if(day > 1) 
              printf("\n  And a Partridge in a Pear Tree");
              printf("\n  A Partride in a Pear Tree");
        if(day < 12) {
          printf("\n\n\t\t   press enter to see the next day's presents");
      printf("\n\n\t\t\t     press enter when ready");
      day = getchar();
      return 0;

  2. #2
    Registered User
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    Apr 2009
    Nice ,

  3. #3
    and the hat of int overfl Salem's Avatar
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    Aug 2001
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    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  4. #4
    and the hat of sweating
    Join Date
    Aug 2007
    Toronto, ON
    Quote Originally Posted by Salem View Post
       register n = (count + 7) / 8;      /* count > 0 assumed */
       switch (count % 8)
       case 0:        do {  *to = *from++;
       case 7:              *to = *from++;
       case 6:              *to = *from++;
       case 5:              *to = *from++;
       case 4:              *to = *from++;
       case 3:              *to = *from++;
       case 2:              *to = *from++;
       case 1:              *to = *from++;
                          } while (--n > 0);
    I don't get it. If count % 8 is anything other than 0, shouldn't you have a do-while loop that's missing the do part?
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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  5. #5
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Quote Originally Posted by cpjust
    If count % 8 is anything other than 0, shouldn't you have a do-while loop that's missing the do part?
    No, you would not. The case labels are just labels, so you can imagine a situation where a goto jumps into the middle of a do while loop.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
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