sorting structure elements in C - c

Question

I have the following code, in which I must sort book titles by alphabetical order. this is the code I have and am unsure of how to perform the actual sort. any help regarding how to sort more than 2 books would also be appreciated, because the user is prompted to enter up to 30 books.
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
struct Books
{
char title[256];
char author[256];
char genre[256];
int qualityRATE;
int pages;
};
int numberbook = 1;
int casee;
int booksnumber;
int i;
int main()
{
char again;
do
{
printf("how many books will you be entering today?");
scanf("%i", &booksnumber);
printf("Enter the information for your book.\n Name\n Author\n Genre\n quality rating\n\n");
struct Books book1;
struct Books book2;
scanf("%s", book1.title);
scanf("%s", book2.title);
printf("The title of book %i is: %s\n", numberbook, book1.title);
printf("The title of book %i is: %s\n", numberbook, book2.title);
printf("how would you like to sort?\n 1: By title\n 2: by Author\n 3: by pages\n\n");
scanf("%i", &casee);
switch(casee)
{
case 1:
for(i = 1; i < booksnumber, i++;)
{
if(strcmp(book[i].title, book[i+1].title) < 0)
strcpy(book[i+1].title, book[i].title);
else
if(strcmp(book[i+1].title, book[i].title) < 0)
strcpy(book[i].title, book[i+1].title);
}
printf("\n%s\n", book1.title);
break;
case 2:
break;
}
printf("Another book?\n");
numberbook++;
scanf("%s", &again);
}
while(again == 'y');
return 0;
}

Answer 1

I see in your code some problems:
You have to initialize an array of book structures, not book1 and book2, declaring:
struct books book[nnn] /* where nnn is the maximum number of book */
You have to use a counter (should be booksnumber) starting from 0 into the do while loop
You have to use scanf using book[booksnumber] and increment booksnumber for each scanf.
If you want a solid sort engine I suggest you to use the function qsort (qsort is a C library function in stdlib.h)
see: www.cplusplus.com/reference/cstdlib/qsort
A correct way to sort the item should be that in the following code:
struct Books app;
int i,j;
for(i=0;i<booksnumber;i++) {
for(j=i+1;j<booksnumber;j++) {
if (strcmp(book[i].title,book[j].title)<0) {
app=book[i];
book[j]=book[i];
book[i]=app;
}
}
}
I think that the first for loop should be better as below, but I have written this code on the fly and then I have not verified its behavour.
for(i=0;i<booksnumber-1;i++)
I've not verified if the direction of the sort is as you require, if is not you may change the "sign" of the comparation inverting it. IE:
if (strcmp(book[i].title,book[j].title)>0)

Answer 2

For just two books you can use swap. And I think you also need to swap all book properties, not just its title :
void swapBook(struct Books *a, struct Books *b) {
struct Books c = *a; /* backup first book */
*a = *b; /* replace first book with second book */
*b = c; /* replace second book with the backup of first book */
}
Then you should be able to use it like this:
if ( strcmp(book[i].title, book[i+1].title) < 0 ) {
swapBook( &book[i], &book[i+1] );
}
For more than two books, this is not going to work, you need to use qsort.