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Use of Pointers for implementing list of elements

The first part of the code is List.h

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//**********************************************
// List.h
//**********************************************
#ifndef LIST_H
#define LIST_H
#include
#include
using namespace std;
class List{
public :
       List();//Constructor
       ~List();//Destructor
       void addItem(int item);//add integer item
       void deleteItem(int loc);//delete item
private:
       int *ptr,size;//pointer and its size
};
#endif

This part of the code is List.cpp

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#include "List.h"
List::List(){
     size = 0;//We inialize size to 0
     //since initial size is 0
}
//addItem method which adds an item to
//the end of the list just like arrayList
void List::addItem(int item){
     //if size is 0 create an array
     if(size==0){
         ptr= new int[++size];
         ptr[size-1] = item;
     }
     //if size is not zero
     else{
         //we inialize a pointer which have size
         //of size+1 since we want to add one more
         //item to the end of the list
         int *newPtr;
         newPtr = new int [size+1];
         //we put the elements into new array
         for(int i=0;i<size;i++)
             newPtr[i] = ptr[i];
         //we lastly insert the item to the end of
         //the list
         newPtr[size++] = item;
         //we delete the ptr pointer's elements
         //since they use memory
         delete [] ptr;
         //Lastly we use address of newPtr for ptr
         ptr = newPtr;
     }
}
//deleteItem method which deletes an item by given
//location which specify array position.
void List::deleteItem(int loc){
     //we inialize a pointer which have size
     //of size-1 since we want to delete one
     //item which is on location loc
     int *newPtr;
     newPtr = new int [size--];
     //we put the elements into newPtr until
     //we come accross to the given location
     for(int i=0;i<loc-1;i++)
         newPtr[i] = ptr[i];
     //after that we do not put the ptr[loc]
     //so that it will be deleted
     for(int i=loc;i<size;i++)
         newPtr[i] = ptr[i+1];
     //we delete the ptr pointers' elements
     //since they use memory
     delete [] ptr;
     //Lastly we use address of newPtr for ptr
     ptr = newPtr;
}
//Destructor
List::~List(){
     //we delete the ptr pointers' elements
     //since they use memory
     delete [] ptr;     
}

2 Comments

  1. bk bk

    Are you sure the “delete[], delete” thing is not wrong? Something tells me this is a double delete on the same pointer. Also, this class could benefit if you allocated memory in chunks (have a “size” member and “allocated_size”, allocate e.g. 1024 bytes more when when “size” >= “allocated_size” and vice versa when freeing memory).

  2. Yusuf Aytaş Yusuf Aytaş

    Thank you very much for your attention. The first delete [] ptr is to delete array elements. The second one is not necessarry and we delete ptr. Yout are right about “size” and “allocated_size”. However, I wanted to show people the use of pointers and I did not care efficiency. It will be more beneficial if we use chunks.
    Thank you very much…

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