0x0E-structures_typedef

0x0E. C - Structures, typedef

Structures (also called structs) are a way to group several related variables into one place. Each variable in the structure is known as a member of the structure.

Unlike an array, a structure can contain many different data types (int, float, char, etc.).

---

Create a Structure

You can create a structure by using the struct keyword and declare each of its members inside curly braces:

struct MyStructure {   // Structure declaration  
  int myNum;           // Member (int variable)  
  char myLetter;       // Member (char variable)  
}; // End the structure with a semicolon

To access the structure, you must create a variable of it.

Use the struct keyword inside the main() method, followed by the name of the structure and then the name of the structure variable:

Create a struct variable with the name "s1":

struct myStructure {  
  int myNum;  
  char myLetter;  
};

int main() {  
  struct myStructure s1;
  return 0;  
}

---

Access Structure Members

To access members of a structure, use the dot syntax (.):

Example

// Create a structure called myStructure  
struct myStructure {  
  int myNum;  
  char myLetter;  
};

int main() {  
  // Create a structure variable of myStructure called **s1**  
  struct myStructure s1;

  // Assign values to members of s1  
  s1.myNum = 13;  
  s1.myLetter = 'B';

  // Print values  
  printf("My number: %d\n", s1.myNum);  
  printf("My letter: %c\n", s1.myLetter);

  return 0;  
}

Now you can easily create multiple structure variables with different values, using just one structure:

Typedef

The C language contains the typedef keyword to allow users to provide alternative names for the primitive (e.g.,​ int) and user-defined​ (e.g struct) data types.

Remember, this keyword adds a new name for some existing data type but does not create a new type.

typedef & struct

Using typedef struct results in a cleaner, more readable code, and saves the programmer keystrokes​. However, it also leads to a more cluttered global namespace which can be problematic for large programs.

You can use typedef to give a name to your user defined data types as well. For example, you can use typedef with structure to define a new data type and then use that data type to define structure variables directly as follows −

typedef struct student_structure{
    char* name;
    char* surname;
    int year_of_birth;
} student;

Tasks

0. Poppy

Define a new type struct dog with the following elements:

• name, type = char *
• age, type = float
• owner, type = char *

solution

1. A dog is the only thing on earth that loves you more than you love yourself

Write a function that initialize a variable of type struct dog

• Prototype: void init_dog(struct dog *d, char *name, float age, char *owner);

solution

2. A dog will teach you unconditional love. If you can have that in your life, things won't be too bad

Write a function that prints a struct dog

• Prototype: void print_dog(struct dog *d);
• Format: see example bellow
• You are allowed to use the standard library
• If an element of d is NULL, print (nil) instead of this element. (if name is NULL, print Name: (nil))
• If d is NULL print nothing.

solution

3. Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read

Define a new type dog_t as a new name for the type struct dog.

solution

4. A door is what a dog is perpetually on the wrong side of

Write a function that creates a new dog.

• Prototype: dog_t *new_dog(char *name, float age, char *owner);
• You have to store a copy of name and owner
• Return NULL if the function fails

solution

5. How many legs does a dog have if you call his tail a leg? Four. Saying that a tail is a leg doesn't make it a leg

Write a function that frees dogs.

• Prototype: void free_dog(dog_t *d);

[solution](5-free_dog.c

)