04 Composite data types as structures

1. A structure is a user defined composite data type in C.
2. A structure is used to group items of possibly different types into a single type.
3. Unlike Java/C++ classes, structures do not have member functions.

struct tag_name {
	T1 member1;
	T2 member2;
	/* declare as many members as desired,
	but the entire structure size must be
	known to the compiler. */
};

Example 1: Point with x and y coordinates

• A point has two coordinates x and y.
• In C we can create a new data-type Point as

struct Point
{
	int x, y
};
 
int main() 
{
	struct Point p1;  // p1 is an object of type Point
}

• There is a shortcut of struct Point p1 i.e., add typedef before struct.
• Structure members are accessed using the dot (.) operator.

typedef struct Point
{
	int x, y
} Point;
 
int main() 
{
	Point p1;  // p1 is an object of type Point
	// for p1(2,3)
	p1.x = 2;
	p1.y = 3;
}

Pointer to a structure object

• We can create pointers to point to structure objects.
• If we have a pointer to structure, members are accessed using arrow (->) operator. s->x is a shortcut for (*s).x.
• Example : Lists

tyepdef struct list_t 
{
	int elem;
	struct list *next;
} list_t;
 
list_t *myList;
myList = malloc(sizeof(list_t));
myList->elem = 4;
myList->next = NULL;