Sorting numbers in a file

This is a discussion on Sorting numbers in a file within the C Programming forums, part of the General Programming Boards category; >>quicksort(array, s); You don't want to sort the whole array, only the elements that have real data in them, so ...

  1. #16
    End Of Line Hammer's Avatar
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    >>quicksort(array, s);
    You don't want to sort the whole array, only the elements that have real data in them, so use:
    >>quicksort(array, i);

    Change this bit:
    Code:
    while(array != NULL){      //Puts the numbers back into a new file
          for(n=0; n <101; n++){
              fprintf(quick, "%d\n", array[n]);
          }
        }
    to this (note, no "while" loop needed)
    Code:
    for (n = 0; n < i; n++)
      {
        fprintf(quick, "%d\n", array[n]);
      }
    Change this
    >>for(b=a=1;b<size;b++){
    to this
    for (b = a; b < size; b++)

    See how you go, that may not be all necessary changes, but it should get you moving.
    When all else fails, read the instructions.
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  2. #17
    Registered User
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    Wow, I didn't even see those things. Thanks for the start.

    Actually, those things fixed the whole program. Thanks.

  3. #18
    Been here, done that.
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    For loop is not appropriate in this case.
    Code:
    for (i=0; fgets(buf,sizeof(buf),fp) && i < 101; i++){
      array[i]=atoi(buf);
    }
    Use this:
    Code:
    i = 0;
    while (fgets(buf,sizeof(buf),fp) != EOF)
    {
        array[i++]=atoi(buf);
    }
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  4. #19
    Ultraviolence Connoisseur
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    Quote Originally Posted by WaltP
    For loop is not appropriate in this case.
    Code:
    for (i=0; fgets(buf,sizeof(buf),fp) && i < 101; i++){
      array[i]=atoi(buf);
    }
    Use this:
    Code:
    i = 0;
    while (fgets(buf,sizeof(buf),fp) != EOF)
    {
        array[i++]=atoi(buf);
    }
    this could cause an overflow as you didnt add the i < 101...also i gets incremented past the end of the array on the last recursion (if there is 100 numbers) so if you referance array[i] again after the loop without changing i, it would cause undefined behavior.

    Why isnt a for loop apporiate? do you just have a general distaste for for loops, or what?

  5. #20
    Code Goddess Prelude's Avatar
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    >while (fgets(buf,sizeof(buf),fp) != EOF)
    You probably meant NULL instead of EOF.

    >For loop is not appropriate in this case.
    Why not? It still counts a set number of times unless end of file is reached or an error occurs. If it makes you feel better then you can move fgets out of the loop condition to get something more idiomatic (albeit also more verbose):
    Code:
    for (i=0; i < 101; i++){
      if (fgets(buf,sizeof(buf),fp) == NULL)
        break;
      array[i]=atoi(buf);
    }
    My best code is written with the delete key.

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