Trying to replace an element of a string array but only able to input a new string in that position. C++

Question

Hello I am attempting to create a very simplified inventory system and I am having a slight issue. When trying to change an element in my string array, I am instead putting a new string value into the existing array and pushing everything else forwards.

// ConsoleApplication2.cpp : Defines the entry point for the console application.

#include "stdafx.h"
#include <iostream>
#include <string>

int main()
{
    const int maxItems = 10; //Maximum number of items inventory can hold
    int numbItems = 0; //number of current items

    std::string inventory[maxItems]; //inventory

    //Items in inventory
    inventory[++numbItems] = "Sword";
    inventory[++numbItems] = "Cloak";
    inventory[++numbItems] = "Boots";

    //Show player items in inventory
    for (int i = 0; i <= numbItems; ++i)
    {
        std::cout << inventory[i] << "\n";
    }


    inventory[0] = "Axe"; //Replace sword with axe

    //Show player items in inventory
    for (int i = 0; i <= numbItems; ++i)
    {
        std::cout << inventory[i] << "\n";
    }


    //keep window open
    std::string barn;
    std::cin >> barn;

    return 0;
}

This code outputs; "axe, sword, cloak and boots" when the desired result is "axe, cloak and boots".

Thank you in advance.

A.Franzen · Accepted Answer · 2015-11-05 12:07:14Z

3

You use the preincrement-operator to fill your array.

inventory[++numbItems] = "Sword";

As numbItems starts at 0, you insert your first element at 1.

Just use the post-increment, and it will work fine.

answered Nov 5, 2015 at 12:07

A.Franzen

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2 Comments

Ryan Swann Over a year ago

Thank you! Are there any detailed explanations about pre/post increment that I can read to properly understand it?

A.Franzen Over a year ago

Any introductory text for c / c++ / c# should do. The mechanism is the same in all c-derived languages. Personally I prefer the Kernighan Richie when teaching, it's short, concise and well written. en.wikipedia.org/wiki/The_C_Programming_Language

alexeykuzmin0 · Accepted Answer · 2015-11-05 12:06:23Z

3

As far as I can see from your code, the numbItems for sword is 1 (you use pre-increment). Probably using post-increment will fix your problem.
Try using the code below (live IdeOne code):

// ConsoleApplication2.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <iostream>

#include <string>

int main()
{
    const int maxItems = 10; //Maximum number of items inventory can hold
    int numbItems = 0; //number of current items

    std::string inventory[maxItems]; //inventory

    //Items in inventory
    inventory[numbItems++] = "Sword";
    inventory[numbItems++] = "Cloak";
    inventory[numbItems++] = "Boots";

    //Show player items in inventory
    for (int i = 0; i <= numbItems; ++i)
    {
        std::cout << inventory[i] << "\n";
    }


    inventory[0] = "Axe"; //Replace sword with axe

    //Show player items in inventory
    for (int i = 0; i <= numbItems; ++i)
    {
        std::cout << inventory[i] << "\n";
    }


    //keep window open
    std::string barn;
    std::cin >> barn;

    return 0;
}

On my computer, this works (the output is Sword,Cloak,Boots and Axe,Cloak,Boots).

answered Nov 5, 2015 at 12:06

alexeykuzmin0

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1 Comment

Ryan Swann Over a year ago

Thank you! Are there any detailed explanations about pre/post increment that I can read to properly understand it?

Rajdeep Paul · Accepted Answer · 2015-11-05 12:22:44Z

Change the pre-increment operator to post-increment operator and you'll get your desired result. Here's the code,

#include "stdafx.h"
#include <iostream>
#include <string>

int main()
{
    const int maxItems = 10; //Maximum number of items inventory can hold
    int numbItems = 0; //number of current items

std::string inventory[maxItems]; //inventory

//Items in inventory
inventory[numbItems++] = "Sword";
inventory[numbItems++] = "Cloak";
inventory[numbItems++] = "Boots";

//Show player items in inventory
for (int i = 0; i < numbItems; ++i)
{
    std::cout << inventory[i] << "\n";
}


inventory[0] = "Axe"; //Replace sword with axe

//Show player items in inventory
for (int i = 0; i < numbItems; ++i)
{
    std::cout << inventory[i] << "\n";
}

return 0;

}

Also note that since your array starts with 0th index, it should be i < numbItems in the for loop rather than i <= numbItems

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