Program doesn't prompt user for last input, but loops for second book - Data structures

Question

I\'m learning about data structures. I\'ve written a simple program that asks the user to fill in information on a 3 book purchase. Like name of book, author, cost and pages.

Answer 1

Your first scanf call fails if you do not exactly type in the $ before the amount. As a result, scanf immediately returns, and the second scanf reads the input that should have went to the previous scanf call.

Edit: Sorry, I didn't provide the source for the information. According to the man page for scanf(3):

The format string consists of a sequence of directives which describe how to process the sequence of input characters. If processing of a directive fails, no further input is read, and scanf() returns. A "failure" can be either of the following: input failure, meaning that input characters were unavailable, or matching failure, meaning that the input was inappropriate (see below).

Answer 2

Change like this

 for(ctr = 0; ctr < 3; ctr++)
    {
        printf("What is the name of the book #%d?\n", (ctr+1));
        gets(books[ctr].title);
        puts("Who is the author? ");
        gets(books[ctr].author);
        puts("How much did the book cost? ");
        scanf("%lf$", &books[ctr].price); //Changed
        puts("How many pages in the book? ");
        scanf(" %d", &books[ctr].pages);
        getchar();  // Clears last newline for the next loop
    }

scanf man page

Answer 3

i edited your code by using file processing functions. and it is a good way since it omits all the invalid inputs the user may enter after its answers. like:

75467 jhfjkghsj;kfjgklj

here is your edited code:

struct bookinfo {
    char title[40];
    char author[25];
    double price;
    int pages;
}; // Header File "bookinfo"

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
    int ctr;
    struct bookinfo books[3]; // Array of three structure variables

    // Get the information about each book from the user

    for(ctr = 0; ctr < 3; ctr++)
    {
        printf("What is the name of the book #%d?\n", (ctr+1));
        gets(books[ctr].title);
        fseek(stdin,0,SEEK_END);
        puts("Who is the author? ");
        gets(books[ctr].author);
        fseek(stdin,0,SEEK_END);
        puts("How much did the book cost? ");
        scanf(" $%f", &books[ctr].price);
        fseek(stdin,0,SEEK_END);
        puts("How many pages in the book? ");
        scanf(" %d", &books[ctr].pages);
        fseek(stdin,0,SEEK_END);
    }
    // Print a header line and then loop through and print the info
    printf("\n\nHere is the collection of books: \n");
    for(ctr = 0; ctr < 3; ctr++)
    {
        printf("#%d: %s by %s", (ctr+1), books[ctr].title, books[ctr].author);
        printf("\nIt is %d pages and cost $%.2f", books[ctr].pages, books[ctr].price);
        printf("\n\n");
    }
    return (0);
}

I've added the fseek function after every input. this function moves the file pointer to the place you want. here, 0 offset from the end of stdin