Why dynamic memory is needed - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use dynamic memory allocation in C?

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

A To improve the speed of the program by using static memory only.

B To allocate memory at compile time for fixed-size variables.

C To avoid using pointers and arrays in the program.

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

💡 Hint

Think about when the program needs memory but does not know how much it will need before running.

Dynamic memory allocation allows a program to request memory while it is running, which is useful when the amount of memory needed cannot be determined before the program starts.

❓ Predict Output

intermediate

Output of dynamic memory allocation example

What is the output of the following C code?

C

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = (int *)malloc(3 * sizeof(int));
    if (ptr == NULL) {
        printf("Memory allocation failed\n");
        return 1;
    }
    ptr[0] = 10;
    ptr[1] = 20;
    ptr[2] = 30;
    printf("%d %d %d\n", ptr[0], ptr[1], ptr[2]);
    free(ptr);
    return 0;
}

A 10 20 30

B Memory allocation failed

C 0 0 0

D Compilation error

💡 Hint

Check if memory allocation was successful and values assigned before printing.

The program allocates memory for 3 integers, assigns values, and prints them. Since allocation succeeds, it prints '10 20 30'.

❓ Predict Output

advanced

What happens if malloc fails?

What will be the output of this C program if malloc fails to allocate memory?

C

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = (int *)malloc((size_t)1000000000000 * sizeof(int));
    if (ptr == NULL) {
        printf("Allocation failed\n");
    } else {
        printf("Allocation succeeded\n");
        free(ptr);
    }
    return 0;
}

A Allocation succeeded

B Allocation failed

C Compilation error due to large size

D Program crashes without output

💡 Hint

Consider what happens when malloc cannot find enough memory.

If malloc cannot allocate the requested memory, it returns NULL, so the program prints 'Allocation failed'.

🧠 Conceptual

advanced

Why is dynamic memory preferred over static for large data?

Why is dynamic memory allocation preferred over static allocation for large or variable-sized data in C?

A Static memory is faster but limited in size and fixed at compile time.

B Dynamic memory is slower and fixed in size at compile time.

C Dynamic memory allocation does not require freeing memory after use.

D Static memory can only store integers, dynamic memory can store any data type.

💡 Hint

Think about when the program size or data size is not known before running.

Static memory is allocated at compile time and cannot change size, so dynamic memory is used for large or variable data sizes during runtime.

❓ Predict Output

expert

Value of pointer after free() call

What is the value of ptr after calling free(ptr); in this program?

C

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = malloc(sizeof(int));
    *ptr = 42;
    free(ptr);
    printf("%p\n", (void *)ptr);
    return 0;
}

A NULL

B 0

C Address of the freed memory block (non-NULL pointer)

D Compilation error because ptr is used after free

💡 Hint

Does free() change the pointer variable itself?

Calling free() releases the memory but does not change the pointer value. The pointer still holds the address but it is now a dangling pointer.