Invalid delete[] array of pointer - c++

Question

I am learning to create array of pointer and free up memory. This is my simple code
#include <iostream>
using namespace std;
int main()
{
int* classroom[5];
for (int i = 0; i < 5; i++) {
classroom[i] = new int;
}
for (int i = 0; i < 5; i++) {
classroom[i] = &i;
cout<<*classroom[i]<<endl;
}
for (int i = 0; i < 5; i++) {
delete classroom[i];
}
return 0;
}
When I run in valgrind to check for the memory leak, this is the result
==2868== Memcheck, a memory error detector
==2868== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==2868== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==2868== Command: ./m
==2868==
0
1
2
3
4
==2868== Invalid free() / delete / delete[] / realloc()
==2868== at 0x402ACFC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2868== by 0x8048700: main (in /home/student/Downloads/demo/m)
==2868== Address 0xbea69244 is on thread 1's stack
==2868==
==2868==
==2868== HEAP SUMMARY:
==2868== in use at exit: 20 bytes in 5 blocks
==2868== total heap usage: 5 allocs, 5 frees, 20 bytes allocated
==2868==
==2868== LEAK SUMMARY:
==2868== definitely lost: 20 bytes in 5 blocks
==2868== indirectly lost: 0 bytes in 0 blocks
==2868== possibly lost: 0 bytes in 0 blocks
==2868== still reachable: 0 bytes in 0 blocks
==2868== suppressed: 0 bytes in 0 blocks
==2868== Rerun with --leak-check=full to see details of leaked memory
==2868==
==2868== For counts of detected and suppressed errors, rerun with: -v
==2868== ERROR SUMMARY: 5 errors from 1 contexts (suppressed: 0 from 0)
My question is, why I have received the message "invalid free()/delete/delete[]/realloc[]" ? and how to fix it ?
Thanks,

Answer 1

classroom[i] = &i;
should be:
*classroom[i] = i;
You're replacing the pointer that you allocated with new with the address of the local variable i. Then you later try to delete that pointer, but you can't delete local variables, only variables allocated with new. What you actually want to do is copy the value of i into the dynamically allocated variable.

Answer 2

I think the problem is that by the time you delete each classroom it no longer points to the original memory location of the int created by new because you are not pushing the value of i into the memory location of classroom[i], you are actually changing classroom[i] to point to i's memory location.
Try changing
classroom[i] = &i;
to
*(classroom[i]) = i;

Answer 3

In this loop
for (int i = 0; i < 5; i++) {
classroom[i] = &i;
cout<<*classroom[i]<<endl;
}
You are trashing the memory of the array. You set all of the pointers to the address of i and then when the for loop ends i is destroyed and you now have dangling pointers. attempting to delete them is undefined behavior.