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C++ Exercises: Multiply each integer in a list three times

C++ Basic Algorithm: Exercise-125 with Solution

Write a C++ program that multiplies each integer three times to create a new list from a given list of integers.

Test Data:
({1, 2, 3, 4}-> (1 8 27 64}

Sample Solution:

C++ Code :

#include <bits/stdc++.h>
#include <list>

using namespace std;

list<int> test(list<int> nums) {
	       list<int> new_list;
	       list<int>::iterator it;
           for (it = nums.begin(); it != nums.end(); ++it)
            {
                new_list.push_back(*it * *it * *it);                
            }
      return new_list;
}

display_list(list<int> g)
{
    list<int>::iterator it;
    for (it = g.begin(); it != g.end(); ++it)
        cout << *it << ' ';
    cout << '\n';
}

int main() {

  list<int> nums = {1,2,3,4,5,6,7,8,9};
  cout << "Original list of elements:\n";
  display_list(nums);
  list<int> result_list;
  result_list = test(nums);
  cout << "\nNew list from the said list multiplies each integer three times:\n";
  display_list(result_list);
  return 0;
}

Sample Output:

Original list of elements:
1 2 3 4 5 6 7 8 9

New list from the said list multiplies each integer three times:
1 8 27 64 125 216 343 512 729

C++ Code Editor:

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C++ Programming: Tips of the Day

What is the usefulness of `enable_shared_from_this?

It enables you to get a valid shared_ptr instance to this, when all you have is this. Without it, you would have no way of getting a shared_ptr to this, unless you already had one as a member.

class Y: public enable_shared_from_this
{
public:

    shared_ptr f()
    {
        return shared_from_this();
    }
}

int main()
{
    shared_ptr p(new Y);
    shared_ptr q = p->f();
    assert(p == q);
    assert(!(p < q || q < p)); // p and q must share ownership
}

The method f() returns a valid shared_ptr, even though it had no member instance. Note that you cannot simply do this:

class Y: public enable_shared_from_this
{
public:

    shared_ptr f()
    {
        return shared_ptr(this);
    }
}

The shared pointer that this returned will have a different reference count from the "proper" one, and one of them will end up losing and holding a dangling reference when the object is deleted.

Ref : https://bit.ly/3pwVzzz