Unexpected random characters printed by library management program

Question

I am working on a school project where I have to make a program that let the user enter information about new books, delete books or display all registered books.

The unexpected behavior is when I choose to display all books : THE SECOND BOOK'S TITLE ALWAYS print some strange random characters or about 15 empty lines while the rest remain normal.

#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <stdlib.h>

typedef struct {
    int Pages,RlsYear,AtrNbr; //"Pages" stands for "the number of pages", "RlsYear" stands for "Release Year"
    char Title[128],Genre[128],Authors[256];
}book;

int main()
{
    int i,nb;
    char ch1,Tmp[128],cln; 
    book* b = malloc(1 * sizeof(book));

    nb=0;
    puts("\n Enter your choice : ");
    ch1=getch();

    while (ch1 != EOF && ch1 != 'q')
    {
        switch(ch1) {
            case 'n': // N to enter a new book
            case 'N':
            {
                printf("\n enter the book's Title : ");
                gets(b[nb].Title);
                printf(" enter the book's Genre : ");
                gets(b[nb].Genre);
                printf(" how many pages does the book have ? ");
                scanf("%d",&b[nb].Pages);
                gets(cln); //i added those "gets(cln)" to avoid problems from "scanf" so you can just ignore them
                printf(" when was the book released (year)? ");
                scanf("%d",&b[nb].RlsYear);
                gets(cln);
                printf(" how many authors does this book have ? ");
                scanf("%d",&b[nb].AtrNbr);
                gets(cln);
                strcpy(b[nb].Authors,"");

                for(i=0;i<b[nb].AtrNbr;i++)
                {
                    printf("\t\t enter the %d author : ",i+1);
                    gets(Tmp);
                    strcat(b[nb].Authors,Tmp);
                    strcat(b[nb].Authors," | ");
                }
                nb=nb+1;
                book* B = realloc(b, nb+1 * sizeof(book));
                b = B;
            }
            break;

            case 'i': // I to display registered books
            case 'I':
            {
                for(i=0;i<nb;i++)
                    printf("\n %s",b[i].Title);
            }
            break;

             default:
                 printf("unknown choice !");
                 break;
        }
        puts("\n Enter your choice : ");
        ch1=getch();
    }
    return 0;
}

Step 1, Use `int ch1`, not `char ch1` to handle the typically 257 different return values from `getch()`. — chux - Reinstate Monica, Mar 21 '20 at 19:42
Post your _exact_ input. If is like `N`, `'\n'`, `"book title...\n"`, then code has not consumed the `'\n'` before advancing to read the title. So the title becomes `""`. — chux - Reinstate Monica, Mar 21 '20 at 19:44
Where in the world did you find something saying to use `gets()`? That function is so unsafe it's the only one to have been removed from the standard. — Shawn, Mar 21 '20 at 20:13
The compiler might be telling you that `gets(cln);` has the wrong argument type anyway, because `char cln` is not an array. IMO it's a mistake to mix your input methods anyway, and trying to "fix" the behaviour of `scanf`. — Weather Vane, Mar 21 '20 at 20:47
@Shawn when i looked about it here. Actually **gets()** worked fine while **scanf()** caused me a lot of trouble — iyy0v, Mar 22 '20 at 17:21
@WeatherVane even when i removed it, the problem was still there. Also how can i "fix" the behaviour of **scanf**. — iyy0v, Mar 22 '20 at 17:24
@chux-ReinstateMonica But the problem is the error appears only in the SECOND title ! — iyy0v, Mar 22 '20 at 17:25
@Shawn i just tried switching to **scanf()** and the problem is still there ! — iyy0v, Mar 22 '20 at 18:23
You are using `getch()` and `scanf()` and `gets()`. As mentioned, don't mix your methods, and stop using `gets()` completely because it is no longer a C function. Please read [Why is the gets function so dangerous that it should not be used?](https://stackoverflow.com/questions/1694036/why-is-the-gets-function-so-dangerous-that-it-should-not-be-used) — Weather Vane, Mar 22 '20 at 18:40

iyy0v · Accepted Answer · 2020-03-22T19:27:30.817

0

I solved the problem when i changed the b.Title size from 128 to 60. Apparently the problem appears when the b.Title size passes 80. Can someone explain please? i'm more confused now

edited Mar 22 '20 at 19:27

answered Mar 22 '20 at 19:14

iyy0v

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Unexpected random characters printed by library management program

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