C 101: Creating Structures 
Tuesday, August 23, 2022, 03:52 AM - - C Notes
Method 1:
// define it as a template
struct person {
 char first_name[50];
 char last_name[50];
};

// create two instances of person
struct person Person1, Person2;

// assign values to Person1
strcpy(Person1.first_name, "Angel");
strcpy(Person1.last_name, "Cool");

Method 2:
// define it and create two instances of it
struct car {
 char make[50];
 char color[50];
} Car1, Car2;

// assign values to Car1
strcpy(Car1.make, "Chevy");
strcpy(Car1.color, "red");

Method 3:
// use 'typedef' to create it
typedef struct {
 char first_name[50];
 char last_name[50];
} person;

// create two instances of person (no 'struct' keyword needed)
person Person1, Person2;

Method 1 example
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ cat method_1.c 
#include <stdio.h>
#include <string.h>

void main(){
    struct person {
      char first_name[50];
      char last_name[50];
    };

    // create two instances of person
    struct person Person1, Person2;

    // assign values to Person1
    strcpy(Person1.first_name, "Angel");
    strcpy(Person1.last_name, "Cool");
    
    // print assigned values 
    printf("Hello %s %s!\n", Person1.first_name, Person1.last_name);
}
[acool@localhost C-practice]$ gcc method_1.c -o method_1
[acool@localhost C-practice]$ ./method_1 
Hello Angel Cool!
[acool@localhost C-practice]$

Method 2 example
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ cat method_2.c 
#include <stdio.h>
#include <string.h>

void main(){
    // define it and create two instances of it
    struct car {
      char make[50];
      char color[50];
    } Car1, Car2;

    // assign values to Car1
    strcpy(Car1.make, "Chevy");
    strcpy(Car1.color, "red");

    // print assigned values
    printf("My %s %s.\n",Car1.color, Car1.make);
}
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ gcc method_2.c -o method_2
[acool@localhost C-practice]$ ./method_2
My red Chevy.
[acool@localhost C-practice]$

Method 3 example
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ cat method_3.c 
#include <stdio.h>
#include <string.h>

void main(){
    // use 'typedef' to create it
    typedef struct {
      char first_name[50];
      char last_name[50];
    } person;

    // create two instances of person (no 'struct' keyword needed)
    person Person1, Person2;

    // assign values to Person1
    strcpy(Person1.first_name, "Andres Manuel");
    strcpy(Person1.last_name, "Lopez-Obrador");

    printf("Viva la 4T! Viva %s %s!\n", Person1.first_name, Person1.last_name);
}
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ gcc method_3.c -o method_3
[acool@localhost C-practice]$ ./method_3
Viva la 4T! Viva Andres Manuel Lopez-Obrador!
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$


Another example:
[acool@localhost ~]$ 
[acool@localhost ~]$ 
[acool@localhost ~]$ date
Wed Apr  5 02:18:30 PM PDT 2023
[acool@localhost ~]$ 
[acool@localhost ~]$ cat books.c 
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct Books {
    char title[50];
    char author[50];
    char subject[100];
    int id;
};

typedef struct {
    char title[50];
    char author[50];
    char subject[100];
    int id;
} eBooks;

void printdetails(eBooks *myEbook, struct Books *myBook)
{
  printf( "myBook id : %d\n", myBook->id);
  printf( "myBook title : %s\n", myBook->title);
  printf( "myBook author : %s\n", myBook->author);
  printf( "myBook subject : %s\n", myBook->subject);
  
  printf("====================================\n");

  printf( "myEbook id : %d\n", myEbook->id);
  printf( "myEbook title : %s\n", myEbook->title);
  printf( "myEbook author : %s\n", myEbook->author);
  printf( "myEbook subject : %s\n", myEbook->subject);
}

int main()
{
    // Pay attention to this! ...two different ways to declare it.
   struct Books *myBook = (struct Books *) malloc(sizeof(struct Books));
   eBooks *myEbook = (eBooks *) malloc(sizeof(eBooks));

   strcpy( myBook->title, "C Programming");
   strcpy( myBook->author, "Angel Cool"); 
   strcpy( myBook->subject, "Programming C Structs Examples");
   myBook->id = 1;
 
   strcpy( myEbook->title, "C Programming (eBook)");
   strcpy( myEbook->author, "Angel Cool (eBook)"); 
   strcpy( myEbook->subject, "Programming C Structs Examples (eBook)");
   myEbook->id = 2;
 
   printdetails(myEbook,myBook);

   return 0;
}
[acool@localhost ~]$ 
[acool@localhost ~]$ 
[acool@localhost ~]$ gcc books.c -o books
[acool@localhost ~]$ 
[acool@localhost ~]$ ./books 
myBook id : 1
myBook title : C Programming
myBook author : Angel Cool
myBook subject : Programming C Structs Examples
====================================
myEbook id : 2
myEbook title : C Programming (eBook)
myEbook author : Angel Cool (eBook)
myEbook subject : Programming C Structs Examples (eBook)
[acool@localhost ~]$ 
[acool@localhost ~]$ file books
books: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=ea1090588d4c761da3060066a7d7a67b7db9caa6, for GNU/Linux 3.2.0, not stripped
[acool@localhost ~]$ 
[acool@localhost ~]$

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