Very simple pointer question

Ok, I have an extremely simple program. This compiles and (as far as I know) it works fine.

Code:

#include <iostream>
#include <conio.h>
using namespace std;
int main() {
	int localvariable = 5;
	int age = 16;
	int * pVariable = &localvariable;
	cout << "Localvariable is " << localvariable << endl;
	cout << "*pVariable points to localvariable " << endl;
	cout << "*pVariable is " << *pVariable << endl;
	cout << "Now I want to change what *pVariable points to " << endl;
	pVariable = &age;
	cout << "Age is " << age << endl;
	cout << "*pVariable = &age" << endl;
	cout << "*pVariable is " << *pVariable << endl;
	getch();
	
	return 0;
}

simple enough. However I never called delete on the pointer, aren't you supposed to always do that? However in this code, when I call delete on pVariable, I get a runtime error

Code:

#include <iostream>
#include <conio.h>
using namespace std;
int main() {
	int localvariable = 5;
	int age = 16;
	int * pVariable = &localvariable;
	cout << "Localvariable is " << localvariable << endl;
	cout << "*pVariable points to localvariable " << endl;
	cout << "*pVariable is " << *pVariable << endl;
	cout << "Now I want to change what *pVariable points to " << endl;
	pVariable = &age;
	cout << "Age is " << age << endl;
	cout << "*pVariable = &age" << endl;
	cout << "*pVariable is " << *pVariable << endl;
	
	delete pVariable; //<--THIS IS THE ONLY CHANGE
	
	getch();
	
	return 0;
}

Why does the top code work, but the bottom code doesn't?

No!!

You only delete pointers to allocated memory! You are not actually deleting the pointer (it can be reused), just the memory...

int i = 10;
int *p = new int;

delete p;

p = new int;

delete p;

p = &i;

...


But warning:

int i = 10;
int *p = new int;

p = &i; //...memory leak! Delete old memory first!

...