new and delete

The new Keyword

The new keyword lets you manage memory yourself.

In the example below, we create memory space for an integer using new, store the value 35 in it, and print it using a pointer:

Example

int* ptr = new int;
*ptr = 35;
cout << *ptr;

Explanation:

• new int creates memory space for one integer
• ptr stores the address of that space
• *ptr = 35; stores the number 35
• cout << *ptr; prints the value

So we used new to create memory, and ptr to access it.

The delete Keyword

When you create something with new, it's your job to remove it when you're done.

To do that, use delete:

Example

delete ptr;

This tells C++: "I'm done with this memory, you can clean it up now."

Note: What Happens If You Forget delete? If you forget to delete memory, your program will still run, but it may use more and more memory over time. This is called a memory leak, and it can slow down or crash your program over time.

Using new and delete with Arrays

You can also use the new keyword to create dynamic arrays.

Note: For arrays, use new[] and delete[]. For single variables, use new and delete.

Dynamic arrays are useful when you don't know the size of the array in advance - like when the size depends on user input or other values that are not known at the start of the program.

For example, imagine you run a hotel. Since you don't know how many guests will arrive, you ask the user for the number and create that many rooms - one to store each guest's name:

Example

#include <iostream>
#include <string>
using namespace std;

int
main() {
  int numGuests;
  cout << "How many guests? ";

cin >> numGuests;

  // Check for invalid input
  if
(numGuests <= 0) {
    cout << "Number of guests must be at
least 1.\n";
    return 0;
  }

  // Create memory space for x
guests (an array of strings)
  string* guests = new string[numGuests];

  // Ignore the leftover newline character after reading numGuests

cin.ignore();

  // Enter guest names
  for (int i = 0; i < numGuests; i++)
{
    cout << "Enter name for guest " << (i + 1) << ": ";
    getline(cin, guests[i]); // Read the full name (including spaces)
  }

  // Show all guests
  cout
<< "\nGuests checked in:\n";
  for (int i = 0; i < numGuests; i++) {

cout << guests[i] << "\n";
  }

  delete[] guests; // Clean
up memory
  return 0;
}

When to Use new

In most cases, you don't need to use new. C++ will automatically handle memory for normal variables like:

int age = 35;
string name = "John";

But sometimes, you have to manage memory yourself - especially when:

• You don't know how much memory you'll need in advance (like how many guests or scores)
• You want to create memory while the program is running, based on user input
• You need to store large or flexible amounts of data
• You want full manual control over memory (e.g., performance-critical code)

In those cases, new helps you create memory, and delete helps you clean it up when you're done.

Tip: If you use new, always remember to use delete (or delete[] for arrays) to avoid memory leaks.