Problem outputting dynamic array from function [closed] - c++

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the function is to preserve argument array and produce anidentical array in the heap memory that has the even elements to (left) & odd(right), but when i output i find a row of zeros and bunch of random big numbers which look like addresses but I don't think they are, Please help.
int* even_left_odd_right(int arr[], int size1)
{
int* array;
array = new int[size1];
for(int i = 0; i < size1; i++)
array[i] = arr[i];
for(int i = 0, j =0; i < size1; i++)
{
if(array[i] % 2 == 0)
{
int temp = array[j];
array[j] = array[i];
array[i] = temp;
j++;
}
}
return array;
}
int main()
{
int size1;
cout << "Enter size of array:";
cin >> size1;
int* array1;
array1 = new int[size1];
int arr[size1];
cout << "Enter the entries in this array: ";
for(int i = 0; i < size1; i++)
cin >> arr[i];
even_left_odd_right(arr, size1);
for(int i = 0; i < size1; i++)
cout << array1[i] << " ";
delete[] array1;
return 0;
}`

Answer 1

The root cause of all your problems is that you do not use the return value of your function. Besides that, there are more things that should be corrected.
Additionally, we need to mention that what you are obviously learning now, dynamic memory management using new and delete and raw pointers for owned memory, is strongly discourage.
Basically: new, delete and raw pointers for owned memory should NEVER be used in C++.
It is that error prone that is has no place any more in standard C++. You even have an error with leaked memory and do not notice it. The array, that you are dynamically allocating in your function with new, is never deleted.
I know that teachers still do teach this crap, but just for explaining dynamic memory mangement from scratch. So, let's go ahead and use it for now.
You have however some additional errors.
Your function returns the partitioned data. But you never use the functions return value
You are using (for whatever reason??) a so called VLA (Variable Length Array) in int arr[size1];. This is illegal in C++. Real C++ compilers will not allow that.
You are mixing up arr and array1. In the beginning, you are creating array1. After creation, it is not initialized and will contain random values.
Then you call your function with arr and output array1 at the end. So, you will output random data. That is, what you see. Random data.
You could use the build in std::swap function. But I guess that it is prohibited by the teacher. What a shame.
You unneccessarily change the order of the entries in the array with swapping. But this does not harm
Your function simply returns a raw pointer. The outer world does not know anything about that. That is dangerous
You even do not know that arr in your function signature (int arr[]) will decay to a pointer
To quickly fix your code, we could write:
#include <iostream>
int* even_left_odd_right(int arr[], int size1)
{
int* array;
array = new int[size1];
for (int i = 0; i < size1; i++)
array[i] = arr[i];
for (int i = 0, j = 0; i < size1; i++)
{
if (array[i] % 2 == 0)
{
int temp = array[j];
array[j] = array[i];
array[i] = temp;
j++;
}
}
return array;
}
int main()
{
int size1;
std::cout << "Enter size of array:";
std::cin >> size1;
int* array1;
array1 = new int[size1];
//int arr[size1]; NOT ALLOWED in C++
std::cout << "Enter the entries in this array: ";
for (int i = 0; i < size1; i++)
std::cin >> array1[i];
int* array2 = even_left_odd_right(array1, size1);
for (int i = 0; i < size1; i++)
std::cout << array2[i] << " ";
delete [] array1;
delete [] array2;
return 0;
}
But such code should never be used in C++.
Again, I guess I understand requirements from teacher.
By the way. In C++17 you would probaly write the follwoing code:
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
int main() {
// Tell user, what to do: Get the number of data to operate on
std::cout << "\nEnter the number of data to operate on: ";
// Read the number of data from the user via std::cin. Check, if number is OK
if (size_t numberOfData{}; (std::cin >> numberOfData) and (numberOfData > 0)) {
// Define the vector for our original data with the size given by the user
std::vector<int> dataOriginal(numberOfData);
// And get the number of specified data from the user
std::cout << "\n\nAnd now, please enter the data\n";
std::copy_n(std::istream_iterator<int>(std::cin), numberOfData, dataOriginal.begin());
// We want to preserve the original input, so, make a copy of that vector
std::vector result(dataOriginal);
// Now partition the output as requested
std::stable_partition(result.begin(), result.end(), [](const int i) { return (i % 2) == 0; });
// Show result to user
std::copy(result.begin(), result.end(), std::ostream_iterator<int>(std::cout, " "));
}
else {
std::cerr << "\nError: Wrong input given for number of data\n\n";
}
}
Please note:
No loops
Input validation
CTAD
No function needed, everthing can be done with one statemennt