Special Features of C Language

Enums

enum shape {circle=10, square, rectangle};

shape a = circle;
shape b = square;
shape c = rectangle;

enum gender {female, male};

The same functionality can be achieved using macros. However, macros have global scope. Enums could have local(Inside a function) or global(if outside of all functions) scope.

---

Typedef:

struct node
{
 int data;
 node *link;
};

typedef node N;

N *root = new N;
root->data = 10;
root->link = NULL;

cout << root->data << "\t" << root->link;

---

Bit Fields:

struct employee
{
 unsigned gender: 1; //The colon tells the compiler that we are talking about the bit field
 unsigned id: 4;
 unsigned status: 3;
 unsigned efficient: 2;
};

enum gender {female, mae};
enum id {One,Two};
enum status {Single, Married, Committed};
enum efficient {Yes, No};

int main()
{
 gender gg = female;
 id gi = One;
 status gs = Committed;
 efficient ge = Yes;

 employee e;
 e.gender = gg;
 e.id = gi;
 e.status = gs;
 e.efficient = ge;

 cout << e.gender << endl;
 cout << e.id << endl;
 cout << e.status << endl;
 cout << e.efficient << endl;

 getch();
 return 0;
}

---

Function Pointers:

void display()
{
 cout << "Display\n";
}

int main()
{ 
 void (*fptr)(); //Pointer to a function
 fptr = display; //Pointer now contains the address of the function
 cout << "Address of the function: " << fptr << endl; //Outputing the address of the function
 (*fptr)(); //Invoking the function; //Invoking the function

 getch();
 return 0;
}

Useful for: Dynamically binding a function to the pointer. Dynamically invoking the function too.

---

Function returning pointers:

int* display() //This function is returning a pointer.
{
 cout << "Display\n";
 static int i = 30;
 return(&i); //It will actually be returning the address to an integer
}

int main()
{ 
 int *p;
 p = display();//The address is populated in a pointer variable
 cout << "Address : " << p << "\tValue: " << *p;

 getch();
 return 0;
}

---

Union:

typedef union
{
 int i;
 char c[4];
}test; //This union is not of 8 bytes(4 for int and 4 for chars). It is of 4 bytes only.

int main()
{ 
 test t;
 t.c[0] = 'A'; //The value assigned to the characters will get assigned to the integer i accordingly
 t.c[1] = 'B'; //As the 4 bytes of the characters are shared by the int too. 
 t.c[2] = 'C';
 t.c[3] = 'D'; 
 
 //t.i; // We can't assign value to both the data variables at the same time.
 //This is useful in hardware when sometimes we have to read only 1 value or all the 4 values
 cout << t.c[0] << "\t" << t.c[1] << "\t" << t.c[2] << "\t" << t.c[3] << endl;
 cout << t.i << endl;

 getch();
 return 0;
}