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simple logic in program

johnmerlino (110)
I'm looking at one of exercises from book, and basically this simple program is straightforward, except one thing. There is a conditional check "if (advance(head) == tail)", but in this program it doesn't seem to be needed. When will tail ever be a greater value than head?


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#include <stdio.h>


#include <stdlib.h>



#define MAXQUEUE 1001



int advance(int pointer)

{

  if (pointer < MAXQUEUE - 1)

    return pointer + 1;

  else

    return 0;

}



int main(void)

{

  char blank[MAXQUEUE];

  int head, tail;

  int nonspace;

  int retval;

  int c;



  retval = nonspace = head = tail = 0;

  while ((c = getchar()) != EOF) {

    if (c == '\n') {

      head = tail = 0;

      if (nonspace)

        putchar('\n');

      nonspace = 0;

    }

    else if (c == ' ' || c == '\t') {

      if (advance(head) == tail) {

        putchar(blank[tail]);

        tail = advance(tail);

        nonspace = 1;

        retval = EXIT_FAILURE;

      }



      blank[head] = c;

      head = advance(head);

    }

    else {

      while (head != tail) {

        putchar(blank[tail]);

        tail = advance(tail);

      }

      putchar(c);

      nonspace = 1;

    }

  }



  return retval;

}
kbw (9488)
If you insert and remove elements, the head won't be at the beginning of the list, and it will "wrap around". That's why there is that check.
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