Flash cards
Review the key moves
What is the main idea behind C++ new and delete?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___* ptr = new int;Put the learning moves in the order that makes the concept easiest to apply.
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 :
delete ptr;This tells C++: "I'm done with this memory, you can clean it up now."
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.