Structure of Structs in c

#include <stdio.h>
#include <string.h>
 
struct student_college_detail
{
    int college_id;
    char college_name[50];
};
 
struct student_detail 
{
    int id;
    char name[20];
    float percentage;
    // structure within structure
    struct student_college_detail clg_data;
}stu_data;
 
int main() 
{
    struct student_detail stu_data = {1, "Raju", 90.5, 71145,
                                       "Anna University"};
    printf(" Id is: %d \n", stu_data.id);
    printf(" Name is: %s \n", stu_data.name);
    printf(" Percentage is: %f \n\n", stu_data.percentage);
 
    printf(" College Id is: %d \n", 
                    stu_data.clg_data.college_id);
    printf(" College Name is: %s \n", 
                    stu_data.clg_data.college_name);
    return 0;
}

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

struct book{ //this is like making a datatype of type book
    //these are the fields
  	char name[50];
    char author[50];
    char ISBN[11];
};

int main(){
    struct book book1; //making an instance of book called book1
    /*
    normally to store integers in a struct we can do something like
    book1.number_of_pages = 22; which is correct
    however with character arrays we need to use the strcpy
    function
    */

    strcpy(book1.name, "james and the giant tatti");
    strcpy(book1.author, "Krishan Grewal");
    strcpy(book1.ISBN, "12345678987");

    printf("book name: %s\n", book1.name);
  	printf("book author: %s\n", book1.author);
  	printf("book ISBN: %s\n", book1.ISBN);

return 0;
}

The basic structure

struct [structure_tag]
{
    //member variable 1
    //member variable 2
    //member variable 3
    ...
}[structure_variables];