Guidance Needed For Changing Pre-defined Code

[Jangoon24]

Hey everybody, I'm a little stumped with my current assignment so I'm here for guidance. I need to change a function 'removeAt' to swap a value which the user chooses, with the last element in the list. The program takes in a number of values (ints and strings) from the user and prints them back out.

The assignment is as follows:

"...Because the list elements are in no particular order, you could simply remove the element by swapping the last element of the list with the item to be removed and reducing the length of the list. Rewrite the definition of the function removeAt using this technique."

Here is the first part of the header file that I need to change, I'll include the second half in the next post.

#ifndef H_arrayListType
#define H_arrayListType

#include <iostream>
#include <cassert>

using namespace std;

template <class elemType>
class arrayListType
{
public:
    const arrayListType<elemType>& operator=
                         (const arrayListType<elemType>&);
      //Overloads the assignment operator
    bool isEmpty() const;
      //Function to determine whether the list is empty
      //Postcondition: Returns true if the list is empty; 
      //    otherwise, returns false.
    bool isFull() const;
      //Function to determine whether the list is full.
      //Postcondition: Returns true if the list is full; 
      //    otherwise, returns false.
    int listSize() const;
      //Function to determine the number of elements in the list
      //Postcondition: Returns the value of length.
    int maxListSize() const;
      //Function to determine the size of the list.
      //Postcondition: Returns the value of maxSize.
    void print() const;
      //Function to output the elements of the list
      //Postcondition: Elements of the list are output on the 
       //   standard output device.
    bool isItemAtEqual(int location, const elemType& item) const;
      //Function to determine whether the item is the same 
      //as the item in the list at the position specified by
      //Postcondition: Returns true if the list[location] 
      //    is the same as the item; otherwise, 
      //               returns false.
   void insertAt(int location, const elemType& insertItem);
      //Function to insert an item in the list at the 
      //position specified by location. The item to be inserted 
      //is passed as a parameter to the function.
      //Postcondition: Starting at location, the elements of the
      //    list are shifted down, list[location] = insertItem;,
      //    and length++;. If the list is full or location is
      //    out of range, an appropriate message is displayed.
   void insertEnd(const elemType& insertItem);
      //Function to insert an item at the end of the list. 
      //The parameter insertItem specifies the item to be inserted.
      //Postcondition: list[length] = insertItem; and length++;
      //    If the list is full, an appropriate message is 
      //    displayed.
    void removeAt(int location);
      //Function to remove the item from the list at the 
      //position specified by location 
      //Postcondition: The list element at list[location] is removed
      //    and length is decremented by 1. If location is out of 
      //    range,an appropriate message is displayed.
    void retrieveAt(int location, elemType& retItem) const;
      //Function to retrieve the element from the list at the  
      //position specified by location. 
      //Postcondition: retItem = list[location] 
      //    If location is out of range, an appropriate message is
      //    displayed.
    void replaceAt(int location, const elemType& repItem);
      //Function to replace the elements in the list at the 
      //position specified by location. The item to be replaced 
      //is specified by the parameter repItem.
      //Postcondition: list[location] = repItem 
      //    If location is out of range, an appropriate message is
      //    displayed.
    void clearList();
      //Function to remove all the elements from the list. 
      //After this operation, the size of the list is zero.
      //Postcondition: length = 0;
    int seqSearch(const elemType& item) const;
      //Function to search the list for a given item. 
      //Postcondition: If the item is found, returns the location 
      //    in the array where the item is found; otherwise,
      //    returns -1.
    void insert(const elemType& insertItem);
      //Function to insert the item specified by the parameter 
      //insertItem at the end of the list. However, first the
      //list is searched to see whether the item to be inserted 
      //is already in the list. 
      //Postcondition: list[length] = insertItem and length++
      //     If the item is already in the list or the list
      //     is full, an appropriate message is displayed.
    void remove(const elemType& removeItem);
      //Function to remove an item from the list. The parameter 
      //removeItem specifies the item to be removed.
      //Postcondition: If removeItem is found in the list,
      //      it is removed from the list and length is 
      //      decremented by one.

    arrayListType(int size = 100);
      //constructor
      //Creates an array of the size specified by the 
      //parameter size. The default array size is 100.
      //Postcondition: The list points to the array, length = 0, 
      //    and maxSize = size
	
    arrayListType(const arrayListType<elemType>& otherList); 
      //copy constructor

    ~arrayListType();
      //destructor
      //Deallocates the memory occupied by the array.

protected:
    elemType *list;  //array to hold the list elements
    int length;      //to store the length of the list
    int maxSize;     //to store the maximum size of the list
};

[Jangoon24]

template <class elemType>
bool arrayListType<elemType>::isEmpty() const
{
    return (length == 0);
}

template <class elemType>
bool arrayListType<elemType>::isFull() const
{
    return (length == maxSize);
}

template <class elemType>
int arrayListType<elemType>::listSize() const
{
    return length;
}

template <class elemType>
int arrayListType<elemType>::maxListSize() const
{
    return maxSize;
}

template <class elemType>
void arrayListType<elemType>::print() const
{
    for (int i = 0; i < length; i++)
        cout << list[i] << " ";

    cout << endl;
}

template <class elemType>
bool arrayListType<elemType>::isItemAtEqual
                            (int location, const elemType& item) const
{
    return (list[location] == item);
}

template <class elemType>
void arrayListType<elemType>::insertAt
                  (int location, const elemType& insertItem)
{
    if (location < 0 || location >= maxSize)
        cerr << "The position of the item to be inserted "
             << "is out of range" << endl;
    else
        if (length >= maxSize)  //list is full
            cerr << "Cannot insert in a full list" << endl;
        else
        {
            for (int i = length; i > location; i--)
                 list[i] = list[i - 1];   //move the elements down

            list[location] = insertItem;  //insert the item at the 
                                          //specified position

            length++;     //increment the length
    }
} //end insertAt

template <class elemType>
void arrayListType<elemType>::insertEnd(const elemType& insertItem)
{

    if (length >= maxSize)  //the list is full
        cerr << "Cannot insert in a full list" << endl;
    else
    {
         list[length] = insertItem;   //insert the item at the end
         length++;   //increment the length
    }
} //end insertEnd

template <class elemType>
void arrayListType<elemType>::removeAt(int location)
{
    if (location < 0 || location >= length)
        cerr << "The location of the item to be removed "
             << "is out of range" << endl;
    else
    {
        for (int i = location; i < length - 1; i++)
            list[i] = list[i+1];

        length--;
    }
} //end removeAt

template <class elemType>
void arrayListType<elemType>::retrieveAt
                             (int location, elemType& retItem) const
{
    if (location < 0 || location >= length)
        cerr << "The location of the item to be retrieved is "
             << "out of range." << endl;
    else
        retItem = list[location];
} //end retrieveAt


template <class elemType>
void arrayListType<elemType>::replaceAt
                          (int location, const elemType& repItem)
{
    if (location < 0 || location >= length)
        cerr << "The location of the item to be replaced is "
             << "out of range." << endl;
    else
        list[location] = repItem;

} //end replaceAt

template <class elemType>
void arrayListType<elemType>::clearList()
{
    length = 0;
} //end clearList

template <class elemType>
int arrayListType<elemType>::seqSearch(const elemType& item) const
{
    int loc;
    bool found = false;

    for (loc = 0; loc < length; loc++)
        if (list[loc] == item)
        {
            found = true;
            break;
        }

    if (found)
        return loc;
    else
        return -1;
} //end seqSearch

template <class elemType>
void arrayListType<elemType>::insert(const elemType& insertItem)
{
    int loc;

    if (length == 0)   //list is empty
        list[length++] = insertItem;    //insert the item and 
                                //increment the length
    else if (length == maxSize)
        cerr << "Cannot insert in a full list." << endl;
    else
    {
        loc = seqSearch(insertItem);

        if (loc == -1)    //the item to be inserted 
                          //does not exist in the list
            list[length++] = insertItem;
        else
            cerr << "the item to be inserted is already in "
                 << "the list. No duplicates are allowed." << endl;
    }
} //end insert

template<class elemType>
void arrayListType<elemType>::remove(const elemType& removeItem)
{
    int loc;

    if (length == 0)
        cerr << "Cannot delete from an empty list." << endl;
    else
    {
        loc = seqSearch(removeItem);

        if (loc != -1)
            removeAt(loc);
        else
            cout << "The item to be deleted is not in the list."
                 << endl;
    }
} //end remove

template <class elemType>
arrayListType<elemType>::arrayListType(int size)
{
    if (size < 0)
    {
        cerr << "The array size must be positive. Creating "
             << "an array of size 100. " << endl;

        maxSize = 100;
    }
    else
        maxSize = size;

    length = 0;

    list = new elemType[maxSize];
    assert(list != NULL);
}

template <class elemType>
arrayListType<elemType>::~arrayListType()
{
    delete [] list;
}


template <class elemType>
arrayListType<elemType>::arrayListType
                   (const arrayListType<elemType>& otherList)
{
    maxSize = otherList.maxSize;
    length = otherList.length;
    list = new elemType[maxSize]; //create the array
    assert(list != NULL);         //terminate if unable to allocate
                                  //memory space

    for (int j = 0; j < length; j++)  //copy otherList
        list [j] = otherList.list[j];
} //end copy constructor

template <class elemType>
const arrayListType<elemType>& arrayListType<elemType>::operator=
                      (const arrayListType<elemType>& otherList)
{
    if (this != &otherList)   //avoid self-assignment
    {
        delete [] list; 
        maxSize = otherList.maxSize; 
        length = otherList.length; 
 
        list = new elemType[maxSize];  //create the array
        assert(list != NULL);   //if unable to allocate memory 
                                //space, terminate the program 
        for (int i = 0; i < length; i++)
            list[i] = otherList.list[i]; 
    }

    return *this; 
}


#endif 

I've attempted rewriting removeAt multiple times to no avail. I'm not really sure what the assignment is asking honestly. Do I use his replaceAt function inside removeAt? Or am I completely missing the point? Any help would be appreciated. Thanks!

edit: I can include the main source code too if need be.

[norm b]

Hi Jangoon24.

Seems straight forward. Given a list:

1
42
6
5

removeAt(1) - move the last entry (5) to location 1, then shorten list by one, resulting in:

1
5
6

Two lines of code.

[Jangoon24]

Hey norm b,

Thanks for the reply, but I'm not quite sure where I'd be placing removeAt(1). In the main source code it calls remove() to take out the user's choice since that function has removeAt() inside of it. That being said, I used removeAt(1) in place of that but I'm not getting the same results.

Here is the main I'm working with:

#include <iostream>                                       //Line 1

#include <string>                                         //Line 2
#include "arrayListType.h"                                //Line 3

using namespace std;                                      //Line 4

int main()                                                //Line 5
{                                                         //Line 6
    arrayListType<int> intList(100);                      //Line 7
    arrayListType<string> stringList;                     //Line 8

    int number;                                           //Line 9

    cout << "List 10: Enter 5 integers: ";                //Line 10

    for (int counter = 0; counter < 5; counter++)         //Line 11
    {                                                     //Line 12
        cin >> number;                                    //Line 13
        intList.insertAt(counter, number);                //Line 14
    }                                                     //Line 15

    cout << endl;                                         //Line 16
    cout<<"List 19: The list you entered is: ";           //Line 17
    intList.print();                                      //Line 18
    cout << endl;                                         //Line 19

    cout << "Line 20: Enter the item to be deleted: ";    //Line 20
    cin >> number;                                        //Line 21
    intList.remove(number);                               //Line 22
    cout << "Line 23: After removing " << number
         << ", the list is:" << endl;                     //Line 23
    intList.print();                                      //Line 24
    cout << endl;                                         //Line 25

    string str;                                           //Line 26

    cout << "Line 27: Enter 5 strings: ";                 //Line 27

    for (int counter = 0; counter < 5; counter++)         //Line 28
    {                                                     //Line 29
        cin >> str;                                       //Line 30
        stringList.insertAt(counter, str);                //Line 31
    }                                                     //Line 32

    cout << endl;                                         //Line 33
    cout << "Line 34: The list you entered is: " << endl; //Line 34
    stringList.print();                                   //Line 35
    cout << endl;                                         //Line 36

    cout << "Line 37: Enter the string to be deleted: ";  //Line 37
    cin >> str;                                           //Line 38
    stringList.remove(str);                               //Line 39
    cout << "Line 40: After removing " << str
         << ", the list is:" << endl;                     //Line 40
    stringList.print();                                   //Line 41
    cout << endl;                                         //Line 42

    return 0;                                             //Line 43
}                                                         //Line 44 

As you can see in line 22 it calls remove() like I said, and that is where I replaced that line with intList.removeAt(1); but all that did was simply remove the number I picked without swapping anything. Were you trying to get me to change the function in the definition or am I simply just making this harder than it should be and looking over something incredibly simple?

[norm b]

You just need to change the definition of removeAt() in your template class:

template <class elemType>
void arrayListType<elemType>::removeAt(int location)
{
    if (location < 0 || location >= length)
        cerr << "The location of the item to be removed "
             << "is out of range" << endl;
    else
    {
        //for (int i = location; i < length - 1; i++)
        //    list[i] = list[i+1];
        list[location] = list[length-1];
        length--;
    }
} //end removeAt 

Edit: You also need to check to see if it is the last entry being removed.

[Jangoon24]

See, I knew I was stressing myself out and over-thinking it. Thanks norm b for your help, I really appreciate it! It's working flawlessly now thanks to you