Data Structures

Auto variables in different blocks in C

void main()
{
int p=100;
clrscr();
printf("\n P=%d",p);
{
int p=50;
printf("\n P=%d",p);
}
{
int p=40;
printf("\n P=%d",p);
}
printf("\n P=%d",p);
}

Output

P=100
P=50
P=40
P=100

In the above program, the declaration of ‘p’ is made at three places with different values. In the first block, the value of ‘p’ is 100 and the same is displayed on the screen first. In the second block, the value of ‘p’ is 50. The control passes to the second block and ‘p’ is assigned a new value 50 and the same is displayed. When the control goes to third block, ‘p’ is 40 and the displayed value is 40. After it exits from the third block, the value of ‘p’ vanishes, which is initialized in the third block. In the last printf() statement, the value of ‘p’ is 100 which is declared in the first block.

Automatic Variables in C

auto variables are defined inside a function. A variable declared inside the function without storage class name is, by default, an auto variable. These functions are declared on the stack. The stack provides temporary storage. The scope of the variables is local to the block in which they are defined. These variables are available only to the current block or program. Once the executions of the function take place and the return turns off the function, the contents and existence of the auto variables or local variables vanish. Whenever a function is executed, all auto variables are allocated memory, and deallocated when the execution of function ends. The auto variables are safe, i.e. they cannot be accessed directly by other functions.

A keyword auto is used for declaration of automatic variables. By default, every variable pertains to auto storage class.

void main()
{
auto float p=5.5;
clrscr();
call2();
printf("\nP=%2.2f",p);
}
 
void call1()
{
auto float p=10.54;
printf("\nP=%2.2f",p);
}
 
 call2()
 {
 auto float p=20.50;
 call1();
 printf("\nP=%2.2f",p);
 }

Output

P=10.54
P=20.50
P=5.50

Stack implementation with operator overloading in C++

#include <conio.h>
#include <iostream.h>
#include <dos.h>
#include <stdio.h>
#include <conio.h>
 
int  top=0;
 
//class definition
 
class stack
{
    public:
	    int a[];
	    int n;
 
	    stack ();
	    stack operator << (int);
	    stack operator +  (int);
	    stack operator --(void);
}r;
 
//definig the constructor to   initialize
 
    stack :: stack ()
    {
	    clrscr();
	    cout <<"Enter the size of the stack: ";
	    cin >> r.n;
 
	    a[n];
	    top=0;
     }
 
//operator to print
     stack stack::operator << (int top)
     {
	    clrscr();
 
	    if(top == 0)
	    {
		 cout<<"The stack is empty\n";
		 //getch();
	    }
 
	    else
	    {
		 cout<<"The contents of the stack...\n";
 
		 for(int i=top; i>=1; i--)
		 {
			cout<< "------\n";
			cout<< "| " << r.a[i] <<" |\n";
			cout<< "------\n";
		 }
	    }
 
	    return(r);
    }
 
//operator to push to the stack
    stack stack::operator + (int z)
    {
	    if(top == r.n)
	    {
		  cout<<"THE STACK IS FULL YOU CANNOT PUSH..!!\n";
		  getch();
	    }
	    else
	    {
		  top++;
		  a[top] = z;
 
		  r << top;
	    }
 
	    return(r);
     }
 
//operator to pop from	the stack
     stack stack::operator --(void)
     {
	  if(top==0)
	  {
		cout<<"THE STACK IS EMPTY SO CANNOT POP..!!";
	       //getch();
	  }
	  else
	  {
	       cout <<"Element poped is  |" << r.a[top];
	       top = top-1;
	       r << top;
	  }
	  return(r);
     }
 
 
    // main function
 
     void main()
     {
	   int choice;
	   char ch='y';
 
	   while(ch=='Y'||ch=='y')
	   {
		 clrscr();
 
		 cout<<"*** STACK OPERATIONS ***\n" << endl;
		 cout<<" 1-> PUSH    \n";
		 cout<<" 2-> POP     \n";
		 cout<<" 3-> DISPLAY \n";
		 cout<<" 4-> EXIT    \n";
 
		 cin>>choice;
 
		 switch(choice)
		 {
		     case 1:
			    {  int z;
 
			       cout<<"\nEnter the element to be pushed: ";
			       cin>> z;
 
			       r = r + z;  // + operator is overloaded
			       r << top;
 
			       //getch();
			    }
			    break;
 
		     case 2:
			    {
			       //clrscr();
			       r = --r;   // --operator is overloaded
			       r << top;
 
			       (flushall());
			       //getch();
			    }
			    break;
 
		    case 3:
			    {
			       r << top; // << operator is overloaded
 
			       (flushall());
			       //getch();
			    }
			    break;
 
		   case 4:
			    cout<<"IF EXHAUSTED TRY LATER..!!!!";
			    break;
 
		   default:
			    {
			     cout<<"INVALID CHOICE...!!\n";
			     cout<<"Enter choice between 1 and 4 \n";
			    }
			    break;
		}
 
		cout<<"\nDo you want to continue [y/n]?";
		cin>>ch;
	 }
     }

Enter the size of the stack:3
*** STACK OPERATIONS ***

1-> PUSH
2-> POP
3-> DISPLAY
4-> EXIT
1

Enter the element to be pushed: 56
The contents of the stack…
——
| 56 |
——