Pointers and arrays in C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pointer arithmetic with arrays

What is the output of this C code snippet?

C

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40};
    int *p = arr;
    printf("%d\n", *(p + 2));
    return 0;
}

A 30

B 20

C 40

D 10

💡 Hint

Remember that pointer arithmetic moves by the size of the data type.

The pointer p points to the first element of arr. Adding 2 moves it to the third element (index 2), which is 30.

❓ Predict Output

intermediate

Value of pointer after increment

What will be the value printed by this code?

C

#include <stdio.h>

int main() {
    char str[] = "hello";
    char *p = str;
    p++;
    printf("%c\n", *p);
    return 0;
}

A h

B o

C l

D e

💡 Hint

Incrementing a pointer moves it to the next character.

Initially, p points to 'h'. After p++, it points to 'e', so *p is 'e'.

🔧 Debug

advanced

Identify the error in pointer usage

What error does this code produce when compiled or run?

C

#include <stdio.h>

int main() {
    int *p;
    *p = 5;
    printf("%d\n", *p);
    return 0;
}

A Compilation error: uninitialized pointer

B Prints 5

C Segmentation fault (runtime error)

D Undefined behavior but no error

💡 Hint

Consider what happens when you dereference a pointer that has not been assigned a valid address.

Pointer p is uninitialized and points to an unknown memory location. Writing to *p causes a segmentation fault at runtime.

❓ Predict Output

advanced

Output of pointer to array and sizeof

What is the output of this code?

C

#include <stdio.h>

int main() {
    int arr[5] = {1,2,3,4,5};
    int (*p)[5] = &arr;
    printf("%zu\n", sizeof(p));
    return 0;
}

A 8

B 20

C 4

D 5

💡 Hint

sizeof(p) gives the size of the pointer, not the array it points to.

p is a pointer to an array of 5 ints. sizeof(p) returns the size of the pointer itself, typically 8 bytes on 64-bit systems.

🧠 Conceptual

expert

Number of elements accessed via pointer arithmetic

Given the code below, how many elements of the array can be safely accessed using the pointer p?

C

#include <stdio.h>

int main() {
    int arr[4] = {10, 20, 30, 40};
    int *p = arr + 1;
    // How many elements can be accessed safely via p?
    return 0;
}

A 4

B 3

C 2

D 1

💡 Hint

Pointer p points to the second element. Count elements from there to the end.

p points to arr[1]. The array has 4 elements total, so elements at indices 1, 2, and 3 can be accessed safely, totaling 3 elements.