c++ Insert in array algorithm malfunctioning

Question

#include <iostream>
using namespace std;

/* This code is not working as it does not insert the value of item in the
array instead the value of item is zero. But i have troubleshooted this
problem and figured out that the code works fine if i define "int item" as
constant variable or use int i as global variable instead of defining in the
for loop. so my question is what is the reason behind this malfunctioning or
is there any programming secret i haven't aware of yet*/

int main()
{
    int LA[] = {1, 3, 64, 98, 54};
    int k = 3;

    int n = 5;
    int item = 46;
    int j = n;

    for(int i = 0; i < n; i++)
    {   
        cout << "LA[" << i << "] = " << LA[i] << endl;
    }

    n++;

    for( ; j >= k; j-- )
    {
        LA[j+1] = LA[j];
    }

    LA[k] = item;
    cout << endl << "After insertion" << endl << endl;

    for(int i = 0; i < n; i++)
    {
        cout << "LA[" << i << "] = " << LA[i] << endl;
    }

    return 0;
}

int LA[] has fixed size, since its initialization. Look up std::vector. Note that LA[j] for j = 5 is already out of range. — LogicStuff
– LogicStuff, Commented Feb 3, 2016 at 20:01
Please debug your ugly code yourself (or have an const int n = 5;) — user2249683
– user2249683, Commented Feb 3, 2016 at 20:02
And an even more possible duplicate of "Can you resize a C++ array after initialization?" stackoverflow.com/questions/756906/…. Short answer: you can't. If you need a resizeable array, use std::vector. — Topological Sort
– Topological Sort, Commented Feb 3, 2016 at 20:44

Fantastic Mr Fox · Accepted Answer · 2016-02-03 20:10:40Z

0

LA has a fixed size. It is a static array, and you cannot change the size in c or c++. Currently j will be 5 and you will attempt to access LA[5] which is outside the bounds of the array and Undefined Behaviour.

You have 3 options:

Reserve enough space in your static array to hold everything you need: LA[10] = {...
Use dynamic memory and resize: int *LA = new int[10]; (Look this method up)
The best, use a std::vector<int>.

answered Feb 3, 2016 at 20:10

Fantastic Mr Fox

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Comments

inverted_index · Accepted Answer · 2016-02-03 20:10:16Z

0

If you wanna insert item as k'th element of array, You should know that the LA array has not 6th index (LA[6]). So before the second loop, initialize j with n-1. Also if you wanna have all the values, You should use std::vector which can add the values and indexes, dynamically. For further studies about vectors see this link: Here

answered Feb 3, 2016 at 20:10

inverted_index

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