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    <p>One way is to have <em>two</em> global counters: one has the number of books stored, the other gives the next (unique) book id, as Tyler McHenry points out. When you delete a book, decrement the number of books, but never decrement the next book id.</p> <p>I notice that when a book is deleted, you move the rest of the book entries together ("compress" them) so your array is always "dense". So another solution is to add a "deleted" flag to the book structure. Now you don't compress the entries when a book is deleted, but when a book is added, the code must search for an empty place in the array. Also the bookid is just the position in the array. (By the way, if you hard-code sizes, like the size of an array, do it once.)</p> <pre><code>#define MAXSTR (30) struct book { int bookid; int valid; // 1 is valid, 0 is empty or deleted char name[MAXSTR]; char author[MAXSTR]; float price; }; #define MAXBOOKS (40) struct book b[MAXBOOKS]; int findEmpty() { int i; for (i=0; i &lt; MAXBOOKS; i++) { if (! b[i].valid) return i; } return -1; // no more space } void add(void) { int i = findEmpty(); char ch[MAXSTR]; if (i &lt; 0) return; // no room for more books clrscr(); printf("Enter books name:\n"); fgets(b[i].name, MAXSTR, stdin); printf("Enter author's name\n"); fgets(b[i].author, MAXSTR, stdin); printf("Enter price:\n"); fgets(ch, MAXSTR, stdin); b[i].price=atoi(ch); /* Assign the empty location found to this book */ b[i].bookid = i; /* mark that it is valid */ b[i].valid = 1; printf("Dear User,the book has succesfully been added.The book id is %d", b[i].bookid); getch(); } </code></pre> <p>del() now just marks the book as invalid. The main part of del() looks like this.</p> <p>gets(ch); int idToDelete = atoi(ch); // find which structure it belongs to for(i=0;i <p>Use a <a href="http://www.itl.nist.gov/div897/sqg/dads/HTML/selectionSort.html" rel="nofollow noreferrer">selection sort</a> in sort() instead of the one-pass routine (which doesn't work in all cases) which is there. Printing books should skip any book that is not valid, too.</p>
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