Why dynamic memory is needed in C++ - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use dynamic memory in C++?

Which of the following best explains why dynamic memory is needed in C++?

A To allocate memory during program execution when the size is not known beforehand.

B To allocate memory at compile time for fixed size arrays.

C To store constants and literals in the program.

D To improve the speed of the program by using static memory.

💡 Hint

Think about when you don't know how much memory you need before the program runs.

Dynamic memory allows programs to request memory while running, which is useful when the amount of data is not fixed or known in advance.

❓ Predict Output

intermediate

Output of dynamic memory allocation example

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int n = 3;
    int* arr = new int[n];
    for(int i = 0; i < n; i++) {
        arr[i] = i * 2;
    }
    std::cout << arr[2] << std::endl;
    delete[] arr;
    return 0;
}

A 6

B 2

C 4

D 0

💡 Hint

Look at the loop and what values are assigned to each element.

The loop assigns arr[i] = i * 2. For i=2, arr[2] = 2 * 2 = 4.

❓ Predict Output

advanced

What happens if dynamic memory is not freed?

What will happen if you run this C++ code repeatedly without freeing the allocated memory?

C++

#include <iostream>
int main() {
    while(true) {
        int* ptr = new int[1000];
        // no delete[] ptr;
    }
    return 0;
}

A The program will crash or slow down due to memory leak.

B The program will print an error message and stop.

C The program will run forever without any issues.

D The program will free memory automatically after each loop.

💡 Hint

Think about what happens when memory is allocated but never released.

Not freeing dynamic memory causes a memory leak, which can slow down or crash the program as memory runs out.

🧠 Conceptual

advanced

Why can't static arrays always replace dynamic memory?

Why are static arrays not always enough, making dynamic memory necessary?

A Static arrays use more memory than dynamic memory.

B Static arrays are slower than dynamic memory.

C Static arrays can only store integers, dynamic memory can store any type.

D Static arrays have fixed size known at compile time, dynamic memory allows flexible size at runtime.

💡 Hint

Think about when you need to decide the size of an array while the program runs.

Static arrays require size known before running the program. Dynamic memory allows allocating memory based on runtime needs.

🧠 Conceptual

expert

When is dynamic memory allocation most beneficial?

In which scenario is dynamic memory allocation most beneficial?

A When the program does not require any memory allocation.

B When the program needs to handle data whose size changes during execution.

C When the program only uses small amounts of memory once.

D When the program needs to store a fixed number of elements known at compile time.

💡 Hint

Think about programs that grow or shrink data while running.

Dynamic memory is useful when data size is not fixed and can change during program execution.