Pointer arithmetic - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pointer increment on array

What is the output of this C code snippet?

C

#include <stdio.h>

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

A 20

B 10

C 30

D 40

💡 Hint

Incrementing a pointer moves it to the next element in the array.

The pointer p initially points to arr[0] which is 10. After p++, it points to arr[1], which is 20. So, *p prints 20.

❓ Predict Output

intermediate

Pointer subtraction result

What is the output of this C code?

C

#include <stdio.h>

int main() {
    int arr[] = {5, 10, 15, 20, 25};
    int *p1 = &arr[4];
    int *p2 = &arr[1];
    printf("%td\n", p1 - p2);
    return 0;
}

A 3

B 6

C 5

D 4

💡 Hint

Pointer subtraction gives the number of elements between them.

p1 points to arr[4], p2 points to arr[1]. The difference is 4 - 1 = 3 elements.

🔧 Debug

advanced

Identify the error in pointer arithmetic

What error will this C code produce when compiled or run?

C

#include <stdio.h>

int main() {
    int x = 10;
    int *p = &x;
    p = p + 2;
    printf("%d\n", *p);
    return 0;
}

A Compilation error: invalid pointer arithmetic

B Output: 10

C Runtime error: segmentation fault or undefined behavior

D Output: 0

💡 Hint

Pointer arithmetic beyond allocated memory is unsafe.

Adding 2 to pointer p moves it beyond the single int variable x. Dereferencing it causes undefined behavior, often a segmentation fault.

📝 Syntax

advanced

Which pointer arithmetic expression is valid?

Which of the following pointer arithmetic expressions is valid in C?

A p / 2

B p - p

C p * 2

D p + p

💡 Hint

Pointer subtraction between two pointers to the same array is allowed.

You can subtract two pointers (p - p) to get the number of elements between them. Adding two pointers or multiplying/dividing pointers is invalid.

🚀 Application

expert

Calculate sum using pointer arithmetic

What is the output of this C program that sums array elements using pointer arithmetic?

C

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int *p = arr;
    int *end = arr + 5;
    int sum = 0;
    while (p < end) {
        sum += *p++;
    }
    printf("%d\n", sum);
    return 0;
}

A 0

B 10

C 5

D 15

💡 Hint

Pointer p moves from start to end of array, adding each element.

The loop adds all elements: 1+2+3+4+5 = 15. Pointer arithmetic is used to traverse the array.