Function returning array but main showing garbage [duplicate]

Answer 1

this is the perfect code

# include <conio.h>
# include <iostream>
using namespace std;

int * add5ToEveryElement(int arr[], int size)
{
    int *theArray = new int[5];
    for(int i=0; i<size; i++)
    {
        theArray[i] = arr[i] + 5;
        cout<<theArray[i]<<endl;
    }
    return theArray;
}

void main()
{
    const int size = 5;
    int noArr[size];
    for(int i=0; i<size; i++)
    {
        noArr[i] = i;
    }
    int *arr = add5ToEveryElement(noArr, size);
    int *p = arr;
    cout<<endl;cout<<endl;
    for(int i=0; i<size; i++)
    {
        cout<<arr[i]<<endl;
    }
    cout<<endl;cout<<endl;cout<<endl;cout<<endl;
    for(int i=0; i<size; i++)
    {
        cout<<*arr<<endl;
        *arr++;
    }
    getch();
    delete[] p;
}

Answer 2

theArray is a local array in the function add5ToEveryElement() which you are returning to main(). This is undefined behaviour.

Minimally you can change this line:

int theArray[5];

to:

int *theArray = new int[5];

It'll work fine. Don't forget to delete it later in main(). SInce you modify the original pointer, save it:

int *arr = add5ToEveryElement(noArr, size);
int *org = arr;
// Rest of the code

//Finally

 delete[] org;

Answer 3

Returning an array from a function is generally considered bad.

Unless you MUST have a "new" array, I would suggest the typical case in C and C++ is to modify the input array. If the CALLING function wants to have two separate arrays, then it can do so by making it's own copy. Alternatively, you could write your code to have two arrays passed into your function, e.g.

void add5ToEveryElement(int arr[], int arr2[], int size)
{
    for(int i=0; i<size; i++)
    {
        arr2[i] = arr[i] + 5;
        cout<<theArray[i]<<endl;
    }
}

then your main would call with two array arguments, and if you wish to use the same as input and output it will do that too.

Sure, this isn't exactly the answer to your question, but it gives a "better" solution to your problem.

I generally dislike allocation in functions - especially "hidden" allocation (this function says it's adding 5 to every element, not "allocate array with added 5 to each element". Code should never do surprising things, and allocating memory is a little bit of a surprise if you only asked for adding 5 to each element)