simple password based authentication program in c++

#ifdef __linux__
#include <unistd.h>
#endif
#include <iostream>
#include <stdlib.h>
#ifndef __linux__
#include <conio.h>
#endif

using namespace std;

int main()
{
 string pass = "";
#ifdef __linux__
    system("clear");
    pass  = getpass("Enter Password : ");
#else
    system("cls");
    char ch;
    cout << "Enter Password : ";
    ch = _getch();
    while(ch != 13) //character 13 is enter
    {
        pass.push_back(ch);
        cout << '*';
        ch = _getch();
    }
#endif
    if(pass == "Hello")
    {
        cout << "\nAccess granted :P\n";
        //Further processing goes here...
    }
    else
    {
        cout << "\nAccess aborted...\n";
    }
}

Hash Table

//linklist_impl.hpp
#include<string>
using namespace std;
class linklist
{
    int c;
    struct node
    {
    public:
        string data;
        node *link;
    } *p;
public:
    linklist();
    void append(string &str);
    void del(string &str);
    void display();
    string getData();
    int searchlist(string);
    bool isListEmpty();
    ~linklist();
};

//linklist_impl.cpp
#include <iostream>
#include <string>
#include <cstring>
#include "linklist_impl.hpp"
using namespace std;


linklist::linklist()
{
    p = NULL;
    c = 0;
}

void linklist::append(string &str)
{
    node *q, *t;
    if(p==NULL)
    {
        p = new node;
        p->data = str;
        p->link = NULL;
        c += 1;
    }
    else
    {
        q = p;
        while(q->link != NULL)
        {
            q = q->link;
        }
        t = new node;
        t->data = str;
        t->link = NULL;
        q->link = t;
        c += 1;
    }
}

void linklist::del(string &str)
{
    node *q, *r;
    q = p;
    if(q->data == str)
    {
        p = q->link;
        delete q;
        c -= 1;
        return;
    }
    r = q;
    while(q != NULL)
    {
        if(q->data == str)
        {
            r->link = q->link;
            delete q;
            c -= 1;
            return;
        }
        r = q;
        q = q->link;
    }
    cout<<"Element "<<str<<" not found"<<endl;
}

void linklist::display()
{
    node *q;
    int i;
    for(q = p, i = 0; q != NULL, i < c; q = q->link, i++)
    {
        cout<<"\t"<<i<<": "<<q->data<<endl;
    }
}

string linklist::getData()
{
  return p->data;
}

bool linklist::isListEmpty()
{
    node *q;
    int i,flag = 0;
    for(q = p, i = 0; q != NULL, i < c; q = q->link, i++)
    {
      if(q->data != "")
        flag = 1;
    }
    if(flag == 1)
      return false;
    else
      return true;
}

int linklist::searchlist(string searchItem)
{
    node *q;
    int i;
    for(q = p, i = 0; q != NULL, i < c; q = q->link, i++)
    {
      if(q -> data == searchItem)
        return i;
    }
    return -1;
}

linklist::~linklist()
{
    node *q;
    if(p == NULL)
    {
        return;
    }
    while(p != NULL)
    {
        q = p->link;
        delete p;
        p = q;
    }
}


</cstring></string></iostream>

//schashtable.cpp
#include<iostream>
#include<sys/time.h>
#include<stdlib.h>
#include<stdio.h>
#include<limits>
#include<cstring>
#include "linklist_impl.hpp"

using namespace std;
struct timeval starttime,endtime,timediff;
enum {FILLED = 0 , ALL};
const int sizeHTable = 5;


class table
{

private:
    linklist *items;
    int nel;
    int strhash(const char *str);
public:
    table(int size);
    ~table();
    void addItem();
    int searchTable(string);
    void delItem();
    void display( int mode);
    int getCount();
    bool isEmpty();
};

#define BAD_INPUT_CUTOFF 3
unsigned int getIntInRange(unsigned int min, unsigned int max,
                           const char *prompt)
{
    int input, //used to get input
    bad_count=0; //used to keep track of how many bad attempts.
    do
    {
        std::cout << prompt;
        std::cin >> input;
        if (!std::cin.good() || input < min || input > max)
        {
            std::cout << "\nInvalid Input!" << std::endl;
            std::cin.clear(); //resets the state flag
            
//clears out the buffer
std::cin.ignore(std::numeric_limits<std::streamsize>::max(),'\n');
                   
            bad_count++; //User made a bad input, count it
            input = 0;   // user did not enter a valid number
        }
        //See if this is a valid number (users are mean/stupid sometimes)
    }
    while (input == 0 && bad_count < BAD_INPUT_CUTOFF);
    return input;
}


table::table(int size)
{
    items = new linklist[size];
    for(int i = 0; i<sizeHTable ;i++)
    nel = 0;
}

table::~table()
{  
    if(items)
    delete[] items;
}

int table::strhash(const char *str) {
    unsigned long hash = 0;
      int i=0;
        while(i <= strlen(str)) {
              hash = hash + (hash<<5) + (unsigned long)(str[i]);
                  i++;
                    }
          return (hash%sizeHTable); //return the hashed number which must be 
                                    //between 0 an size-1, this is why I used
                                    //hash%size
}

void table::addItem()
{
        string str;
        
        cout<<"\nEnter Data : ";
        cin>>str;

        
        int i = strhash(str.c_str());
        if( i >= 0 && i < sizeHTable )
        {
            items[i].append(str);
            cout<<"\nInserted";
            nel++;
            return;
        }

}

int table::searchTable(string searchItem)
{
    int pos;
    
    int i = strhash(searchItem.c_str());

    if((pos = items[i].searchlist(searchItem)) != -1 )
    {
        cout<<"Bucket["<<i<<"] -> pos : "<<pos<<"\t" <<"\t"<< endl;
        return i;
    }
    else
    {
            cout<<"Data "<<searchItem<<" not present in the table" << endl;
            return -1;
    }
}

void table::delItem()
{
    string item;
    cout<<"\nEnter an item to delete : ";
    cin>>item;
    
    int index;
    index = strhash(item.c_str());
        items[index].del(item);
        nel--;
}

bool table::isEmpty()
{
    if( nel > 0)
    {
        return false;
    }
    else
    {
        cout<<"\nTable is Empty"<<endl;
        return true;
    }
}

void table::display(int mode = FILLED)
{
    if(isEmpty())
        return;

   if(mode == FILLED)
   {
     int i;
     for(i=0; i<sizeHTable; i++)
     { 
        if(items[i].isListEmpty() == false)
        {
          cout<<"Bucket["<<i<<"] :"<<endl;
          items[i].display(); //call the function of our linked list,
                              //which outputs it's records with their indexes
        }
     }
   } 
   else if(mode == ALL)
   {
     int i;
     for(i=0; i<sizeHTable; i++)
     {
        cout<<"Bucket["<<i<<"] :"<<endl;
        items[i].display(); //call the function of our linked list,
                            //which outputs it's records with their indexes
     }
   } 
}

int table::getCount()
{
    return nel;
}

int main()
{
    int choice;
    
    string item;
    table T1(sizeHTable);
    int mode;

    while(1)
    {
        choice = getIntInRange(1,6,"\n1.Add New Item\n2.Delete Item
                 \n3.Search Item \n4.Display Hash Table \n5.Get the
                  number of elements \n6.Exit\nEnter your choice : ");
        
            switch(choice)
            {
            case 1 :
                T1.addItem();
                break;
            case 2 :
                T1.delItem();
                break;
            case 3 :
                if(T1.isEmpty() != true)
                {
                    cout<<"\nEnter an item to search : ";
                    cin>>item;
                    T1.searchTable(item);
                }
                break;
            case 4 :
                cout<<"\nEnter display mode (0 - FILLED / 1- ALL) : ";
                cin>>mode;
                T1.display(mode);
                break;
             case 5 :
                cout<<"Total no. of elements : "<<T1.getCount()<<endl;
                break;
             case 6 :
                exit(0);
            }
        
    }
    
    
}

Virtual Functions

#include <iostream>

using namespace std;

 class Animals{

   public :

     virtual void speak(){

      cout<<"Animals speak random";

    }

};

 

class Dog: public Animals{

  public:

      void speak(){

      cout<<"Dogs woof";

    }

};

 

int main()

{

  Animals *a;

  Dog d;

 

  a = &d;

 

  a->speak();

}

 

Output:

 //without virtual speak()

 Animals speak random

 //with virtual speak()

 Dog woof

LINKED LIST

#include <cstdio>
#include <stdlib.h>
#include <iostream>
#include <limits>
#include <stdio.h>
#define BAD_INPUT_CUTOFF 3

using namespace std;


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

struct searchDS
{
    int occurence;
    int posit[100];
};

typedef struct node Node;
typedef struct searchDS SD;

Node *start = NULL;
Node *new1;

void print_list(Node*);
int print_no();
int count();
unsigned int getIntInRange(unsigned int min, unsigned int max, const char *prompt);

Node* create_node()
{
    Node* newnode;

    newnode = (Node*)malloc(sizeof(struct node));

    printf("\nEnter the data (numeric only): ");
    scanf("%d", &newnode -> data);
    newnode -> next = NULL;

    return newnode;
}

int isEmpty()
{
    if(start == NULL)
    {
        printf("\nList is empty");
        return true;
    }
    else
        return false;
}

Node* search(int data)
{
    Node* ptr;

    int flag = 0;

    for(ptr = start ; ptr; ptr = ptr -> next)
    {
        if(ptr -> data == data)
        {
            flag = 1;
            printf("\nData %d found at %x ",data,ptr);
        }
    }

    if(flag == 1 )
    {
        return ptr;
    }
    else
    {
        printf("\nData %d not found !!!",data);
        return NULL;
    }
}

void adv_search(int data, SD* sp)
{

    Node *ptr,*prev;

    int i ,j, pos = 1;

    if(start ==  NULL)
    {
        printf("\nList is empty ");
        return;
    }
    sp->occurence = 0;

    for(i=0,ptr = start; (ptr); ptr = ptr->next,pos++)
    {
        if(ptr -> data == data)
        {
            (sp->occurence)++;
            sp->posit[i++] = pos ;
        }
    }

    if(sp->occurence == 0)
    {
        printf("\nData %d not in the list!!!",data);
        return;
    }
    printf("\nOcc: %d , Positions : ", sp->occurence);
    for(j=0; j<i; j++)
        printf("%d, ",sp->posit[j]);
    printf("\n");
}

void insert_beg()
{
//printf("\n In function %s\n",__func__);

    new1 = create_node();

    if(start == NULL)
    {
        start = new1;
        print_list(start);
        return;
    }
    else
    {
        new1 -> next = start ;
        start = new1;
        print_list(start);
        return;
    }
}
void insert_end()
{
    Node *ptr,*prev;
//printf("\n In function %s\n",__func__);

    new1 = create_node();

    if(start == NULL)
    {
        start = new1;
        print_list(start);
        return;
    }
    else
    {
        for(prev = start , ptr = start -> next ; ptr ; prev = ptr , ptr = ptr -> next);

        prev -> next = new1;
        print_list(start);
    }
}
void insert_at_pos()
{
    Node *ptr , *prev;
    int pos,i;
//printf("\n In function %s\n",__func__);

    new1 = create_node();

    printf("\nWhat position do you want to enter ? ");
    scanf("%d",&pos);

    if (pos < 1 || pos > print_no())
    {
        printf("\n Inserting failed! Out of bounds!!!");
        return;
    }
    else if(pos == 1)
    {
        new1 -> next = start;
        start = new1;
        print_list(start);
    }
    else if(pos > 1)
    {
        for(i = 1 ,prev = start, ptr = start -> next; (ptr) && (i < pos -1); prev = ptr , ptr = ptr->next,i++);
        prev -> next = new1 ;
        new1 -> next = ptr ;

        print_list(start);
    }
}

void delete_node_by_pos()
{
    Node *prev, *ptr, *temp;
    int pos,i;
    //printf("\n In function %s\n",__func__);

    if(isEmpty() != true)
    {
        printf("\nEnter the node no. you want to delete: ");
        scanf("%d",&pos);

        if (pos < 1 || pos > count())
        {
            printf("\n Deletion failed! Out of bounds!!!");
            return;
        }
        else if(pos == 1)
        {
            temp = start;
            start = start -> next;
            free(temp);
            print_list(start);
        }
        else if(pos > 1)
        {
            for(i = 1 ,prev = start, ptr = start -> next; (ptr) && (i < pos -1); prev = ptr , ptr = ptr->next,i++)
            {
                //`printf("\n prev-> data : %d\tptr->data :%d" ,prev-> data, ptr->data);
            }
            temp = ptr;
            prev -> next = ptr -> next;
            free(temp);
            print_list(start);
        }
    }
}

void delete_node_by_data()
{
    Node *ptr,*prev,*temp;
    int info, ch;
    SD sp;
    static int visited = 0;
    //printf("\n In function %s\n",__func__);

    if(isEmpty() != true)
    {
        printf("\nEnter the data you want to delete: ");
        scanf("%d",&info);
        adv_search(info, &sp);

        {
            if(start -> data == info )
            {
                temp = start;
                start = start -> next;
                free(temp);
                print_list(start);
                return;
            }
            for(prev = start , ptr = start -> next ; ptr ; prev = ptr , ptr = ptr -> next)
            {
                if( ptr -> data == info)
                {
                    temp = ptr;
                    prev -> next = ptr -> next;
                    free(temp);
                    print_list(start);
                    return;
                }
            }
        }
        print_list(start);
    }
}


void print_list(Node* start)
{
    Node *ptr;
//printf("\n In function %s\n",__func__);

    printf("\n");
    for(ptr = start; ptr ; ptr = ptr ->next )
    {
        printf("-> %d ",ptr->data);
    }
    printf("\n");
}
int print_no()
{
//printf("\n In function %s\n",__func__);
    printf("\nThe total no. of members in the list are : %d \n", count());
}

int count()
{

    Node *ptr;
    int count = 0;

    ptr = start ;
    while(ptr!=NULL)
    {
        ptr = ptr -> next;
        count++;
    }

    return count;
}

Node* reverse(Node* root)
{
    Node* ret_val;

    if ( root == NULL || root->next == NULL )
    {
        return root;
    }
    ret_val = reverse ( root -> next );

    root -> next->next = root;
    root->next = NULL;
    return ret_val;
}

unsigned int getIntInRange(unsigned int min, unsigned int max,
                           const char *prompt)
{
    int input, //used to get input
        bad_count=0; //used to keep track of how many bad attempts.
    do
    {
        cout << prompt; //print out our prompt
        cin >> input; //get the input
        if (!cin.good() || input < min || input > max)
        {
            cout << "\nInvalid Input!" << std::endl;
            cin.clear(); //resets the state flag
            cin.ignore(numeric_limits<streamsize>::max(),'\n');
                        //clears out the buffer
            bad_count++; //User made a bad input, count it
            input = 0; // user did not enter a valid number
        }
    }
    while (input == 0 && bad_count < BAD_INPUT_CUTOFF);
    return input;
}

int main()
{
    int choice,searchKey,info;
    SD sp;
    Node* temp;
    while(1)
    {

        printf("\n1.Insert a node at beg\n2.Insert a node at end \n3.Insert a node at a given position\n4.Delete a  node by data\n5.Delete a node by position\n6.Print the list\n7.Print the no. of elements\n8.Reverse the list\n9.Search \n10.Advanced Search\n11.Exit\n");

         choice  = getIntInRange(1,11,"\n Choose your option (1-11):\n");

        switch(choice)
        {
        case 1 :
            insert_beg();
            break;
        case 2 :
            insert_end();
            break;
        case 3 :
            insert_at_pos();
            break;
        case 4 :
            delete_node_by_data();
            break;
        case 5 :
            delete_node_by_pos();
            break;
        case 6 :
            print_list(start);
            break;
        case 7 :
            print_no();
            break;
        case 8 :
            start = reverse(start);
            print_list(start);
            break;
        case 9 :
            printf("\nEnter the data you want to search : ");
            scanf("%d",&searchKey);

            if(search(searchKey)!=NULL)
                printf("\nData %d at %x",searchKey , search(searchKey));

            break;
        case 10 :
            printf("\nEnter the data you want to search : ");
            scanf("%d",&searchKey);
            adv_search(searchKey,&sp);
            break;
        case 11 :
            exit(0);

        default :
            printf("\nInvalid input !!!\n");
            break;

        }
    }
}

Templates in C++

Templates are a way of making your classes more abstract by letting you define the behavior of the class without actually knowing what datatype will be handled by the operations of the class. In essence, this is what is known as generic programming; this term is a useful way to think about templates because it helps remind the programmer that a template class does not depend on the datatype (or types) it deals with. To a large degree, a template class is more focused on the algorithmic thought rather than the specific nuances of a single datatype. Templates can be used in conjunction with abstract data types in order to allow them to handle any type of data. For example, you could make a template stack class that can handle a stack of any datatype, rather than having to create a stack class for every different datatype for which you want the stack to function. The ability to have a single class that can handle several different data types means the code is easier to maintain, and it makes classes more reusable.

The basic syntax for declaring a template class is as follows:

template <class a_type> class a_class {...};

The keyword 'class' above simply means that the identifier a_type will stand for a datatype. NB: a_type is not a keyword; it is an identifier that during the execution of the program will represent a single datatype. For example, you could, when defining variables in the class, use the following line:

a_type a_var;

and when the programmer defines which datatype 'a_type' is to be when the program instantiates a particular instance of a_class, a_var will be of that type.

When defining a function as a member of a templated class, it is necessary to define it as a templated function:

template<class a_type> void a_class<a_type>::a_function(){...}
              

When declaring an instance of a templated class, the syntax is as follows:

a_class<int> an_example_class;
             

An instantiated object of a templated class is called a specialization; the term specialization is useful to remember because it reminds us that the original class is a generic class, whereas a specific instantiation of a class is specialized for a single datatype (although it is possible to template multiple types).

Usually when writing code it is easiest to precede from concrete to abstract; therefore, it is easier to write a class for a specific datatype and then proceed to a templated - generic - class. For that brevity is the soul of wit, this example will be brief and therefore of little practical application.

We will define the first class to act only on integers.

class calc
{
  public:
    int multiply(int x, int y);
    int add(int x, int y);
 };
int calc::multiply(int x, int y)
{
  return x*y;
}
int calc::add(int x, int y)
{
  return x+y;
}

We now have a perfectly harmless little class that functions perfectly well for integers; but what if we decided we wanted a generic class that would work equally well for floating point numbers? We would use a template.

template <class A_Type> class calc
{
  public:
    A_Type multiply(A_Type x, A_Type y);
    A_Type add(A_Type x, A_Type y);
};
template <class A_Type> A_Type calc<A_Type>::multiply(A_Type x,A_Type y)
{
  return x*y;
}
template <class A_Type> A_Type calc<A_Type>::add(A_Type x, A_Type y)
{
  return x+y;
}

To understand the templated class, just think about replacing the identifier A_Type everywhere it appears, except as part of the template or class definition, with the keyword int. It would be the same as the above class; now when you instantiate an
object of class calc you can choose which datatype the class will handle.

calc <double> a_calc_class;

Templates are handy for making your programs more generic and allowing your code to be reused later.