Data Structure about struct array

Question

Recently, I took a subject called Data structure. I've created a program to try out my knowledge but don't know why the program did not work. I can't figure it out so I post it here to ask for solution. I hope people can help me. I am newbie here. So please ignore my opinion if my opinion is found annoying.

#include <stdio.h>
int main()
{
    struct Book
    {
        char title[50];
        int year;
        float price;
    };
    int i;

    struct Book books[50];
    books[0].title="Bullshit";
    books[0].year=132;
    books[0].price=146.9;

    books[1]=(struct Book){"Money",1344,189.4
    };

    for(i=0;i<2;i++)
    {
        printf("Book Title is : %s\n",books[i].title);
        printf("Book Year is %d\n",books[i].year);
        printf("Book price is %3.2f\n",books[i].price);
        printf("\n\n");
    }
}

Answer 1

1 I would make declaration of struct rather outside main than inside

2 Try changing char title[50] to char *title

#include <stdio.h>

struct Book {
    char *title;
    int year;
    float price;
};

int main() {

    int i;

    struct Book books[50];
    books[0].title = "Bullshit";
    books[0].year = 132;
    books[0].price = 146.9;

    books[1] = (struct Book) {"Money", 1344, 189.4
    };

    for (i = 0; i < 2; i++) {
        printf("Book Title is : %s\n", books[i].title);
        printf("Book Year is %d\n", books[i].year);
        printf("Book price is %3.2f\n", books[i].price);
        printf("\n\n");
    }
}

Why it didn't worked before?

In c arrays are not assignable by = operator.
You could do something like instead title[0] = 'B'; title[1] = 'u', etc....(or use strcpy which does it for you).

char *x is not really an array, it's just pointer to single char.
If we write x = "abc", we are telling the compiler: set x to 'a', next byte to 'b', next to 'c', and next to 0(not '0', just zero).

And when you do printf("%s",x), the printf function prints chars from the place in memory specified by x until it see 0 byte.

char *x = "abcd";

char *y = x;
while(*y != 0){   // this loop acts like printf("%s",x);
    printf("%c",*y);
    y++;
}

See also this and this question.

Or if you are using c++, not c, use std::string:

#include <cstdio>
#include <string>

struct Book {
    std::string title;
    int year;
    float price;

    Book(std::string t, int y, float p) {
        title = t;
        year = y;
        price = p;
    }
};

int main() {

    int i;

    Book books[50];
    books[0].title = "Bullshit";
    books[0].year = 132;
    books[0].price = 146.9;

    books[1] = Book(std::string("Money"), 1344, 189.4);

    for (i = 0; i < 2; i++) {
        printf("Book Title is : %s\n", books[i].title.c_str());
        printf("Book Year is %d\n", books[i].year);
        printf("Book price is %3.2f\n", books[i].price);
        printf("\n\n");
    }
}

Answer 2

this

books[0].title="Bullshit";

is not valid. title is defined as char[50]. Either do

strcpy(books[0].title, "BS");

This will copy the bytes of BS to title. Or do

 struct Book
    {
        char *title;
        int year;
        float price;
    };

...
  books[0].title = strdup("BS");

This sets title up as a pointer to a char string. strdup will allocate space for the string and copy BS to that space. You will have to free that allocated space.

Or - the best. Use std::string

 struct Book
    {
        std::string title;
        int year;
        float price;
    };
....
   books[0].title = "BS";

And as a final thought - life goes better with std::vector instead of raw arrays