Dynamically Allocating String Arrays

Question

This is what I have so far. I am trying to edit a dynamically allocated array in C++, however, when the for loop runs, it is skipping over the first item. I need it to get all of the items. Any help is appreciated. Thanks in advance.

#include <iostream>
#include <algorithm>
#include <string>
#include <iomanip>
using namespace std;


int main()
{
    // Declare Variables
    int userChoice = 0;
    int numItems = 0;

    cout << "How many items will be on your list? ";
    cin >> numItems;

    string *list = new string[numItems];

    // Give the user some options
    cout << "1. Add Item" << endl;
    cout << "2. Remove Item" << endl;
    cout << "3. Sort Items" << endl;
    cout << "4. Exit" << endl;
    cout << "Enter the number of the operation you wish to perform: ";
    cin >> userChoice;
    cout << endl;

    // Perform the operation
    switch(userChoice)
    {
    case 1:
        {
            cin.clear();    // Remove new line from cin

            for(int i = 0; i < numItems; i++)
            {
                cout << "Item #" << i + 1 << " --> ";
                getline(cin, list[i]);
            }
        }
        break;
    case 2:
        {

        }
        break;
    case 3:
        {

        }
        break;
    case 4:
        {
            return 0;
        }
    default:
        {
            cout << "Error! Invalid Selection" << endl;
        }

    }

    // Output the list
    cout << "-------Items-------" << endl
         << *list << endl << endl;

    // free memory
    delete [] list;

    cout << "Enter the number of the operation you wish to perform: ";
    cin >> userChoice;


    return 0;
}

Nick Gammon · Accepted Answer · 2016-02-06 02:40:30Z

It seems odd to me to be using the STL for some things (like string) and then use a standard array to hold the strings. Also, list is a standard type of object in STL, so that is not a great name for a variable. This revised code fixes your issues with ignoring the first line, and also uses a vector instead of doing new and delete.

#include <iostream>
#include <algorithm>
#include <string>
#include <iomanip>
#include <vector>
#include <iterator>
using namespace std;

int main()
  {
  // Declare Variables
  int userChoice = 0;
  int numItems = 0;

  cout << "How many items will be on your myList? ";
  cin >> numItems;
  cin.ignore ();

  vector<string> myList;

  while (true)
    {
    // Give the user some options
    cout << "1. Add Item" << endl;
    cout << "2. Remove Item" << endl;
    cout << "3. Sort Items" << endl;
    cout << "4. Exit" << endl;
    cout << "Enter the number of the operation you wish to perform: ";
    cin >> userChoice;
    cin.ignore ();
    cout << endl;

    // Perform the operation
    switch(userChoice)
    {
    case 1:
        {
        for(int i = 0; i < numItems; i++)
            {
            cout << "Item #" << i + 1 << " --> ";
            string s;
            getline(cin, s);
            myList.push_back (s);
            }
        }
        break;
    case 2:
        {

        }
        break;
    case 3:
        {
        sort (myList.begin (), myList.end ());
        }
        break;
    case 4:
        {
            return 0;
        }
    default:
        {
            cout << "Error! Invalid Selection" << endl;
        }

    }

    // Output the myList
    cout << "-------Items-------" << endl;
    copy(myList.begin(), myList.end(), ostream_iterator<string>(cout, "\n"));

  } // end of while
}

The project description explicitly says I can't use standard containers, sort functions, or smart pointers

Redone below to not use those things. :)

#include <iostream>
#include <algorithm>
#include <string>
#include <iomanip>
using namespace std;

int myCompare (const void * a, const void * b)
  {

  if ((*(string *) a) < *(string *) b) return -1;
  if ((*(string *) a) > *(string *) b) return 1;
  return 0;
  }

int main()
  {
  // Declare Variables
  int userChoice = 0;
  int numItems = 0;

  cout << "How many items will be on your myList? ";
  cin >> numItems;
  cin.ignore ();

  string *myList = new string[numItems];

  while (true)
    {
    // Give the user some options
    cout << "1. Add Item" << endl;
    cout << "2. Remove Item" << endl;
    cout << "3. Sort Items" << endl;
    cout << "4. Exit" << endl;
    cout << "Enter the number of the operation you wish to perform: ";
    cin >> userChoice;
    cin.ignore ();
    cout << endl;

    // Perform the operation
    switch(userChoice)
    {
    case 1:
        {
        for(int i = 0; i < numItems; i++)
            {
            cout << "Item #" << i + 1 << " --> ";
            getline(cin, myList [i]);
            }
        }
        break;
    case 2:
        {

        }
        break;
    case 3:
        {
        qsort (myList, numItems, sizeof (string *), myCompare);
        }
        break;
    case 4:
        {
            delete [] myList;
            return 0;
        }
    default:
        {
            cout << "Error! Invalid Selection" << endl;
        }

    }

    // Output the myList
    cout << "-------Items-------" << endl;
    for(int i = 0; i < numItems; i++)
      cout << myList [i] << endl;

  } // end of while
}

This is great, and would be what I would've done but I probably should have been more specific in my initial description. The project description explicitly says I can't use standard containers, sort functions, or smart pointers
Or does qsort count as a sort function? Pfft. How can you sort without using a sort function? Write your own? Then it becomes a sort function.

Christophe · Accepted Answer · 2016-02-06 01:54:53Z

2

The for loop isn't skipping the first element. The first element is just a an empty line.

Because the following clears the error flags.

cin.clear();    // Remove new line from cin --> No!!!!

If you want to skip until the new line you have to use ignore() instead.

cin.ignore(numeric_limits<streamsize>::max(), '\n'); // this removes until newline from cin !

edited Feb 6, 2016 at 1:54

answered Feb 6, 2016 at 1:46

Christophe

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