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 <iostream>
int main() {
    int arr[] = {10, 20, 30, 40};
    int *p = arr;
    std::cout << *(p + 2) << std::endl;
    return 0;
}

A 20

B 40

C 10

D 30

💡 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, which is 30.

❓ Predict Output

intermediate

Value of pointer after increment

What will be the value printed by this program?

C++

#include <iostream>
int main() {
    int arr[3] = {5, 10, 15};
    int *ptr = arr + 1;
    std::cout << *ptr << std::endl;
    ptr++;
    std::cout << *ptr << std::endl;
    return 0;
}

A 10\n15

B 5\n10

C 15\n10

D 10\n10

💡 Hint

Pointer starts at second element, then moves to third.

ptr initially points to arr[1] which is 10, then after ptr++ it points to arr[2] which is 15.

🔧 Debug

advanced

Identify the error in pointer usage

What error will this code produce when compiled or run?

C++

#include <iostream>
int main() {
    int *p;
    *p = 10;
    std::cout << *p << std::endl;
    return 0;
}

A Compilation error: uninitialized pointer

B Runtime error: segmentation fault

C Compilation error: missing semicolon

D Outputs 10

💡 Hint

Think about 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. Dereferencing it causes a runtime segmentation fault.

🧠 Conceptual

advanced

Size of array vs pointer

Given the code below, what will be the output?

C++

#include <iostream>
int main() {
    int arr[5] = {1,2,3,4,5};
    int *p = arr;
    std::cout << sizeof(arr) << " " << sizeof(p) << std::endl;
    return 0;
}

A 20 8

B 20 20

C 5 8

D 5 5

💡 Hint

sizeof(arr) gives total bytes of all elements, sizeof(p) gives size of pointer variable.

arr is an array of 5 ints, each 4 bytes, so 20 bytes total. p is a pointer, typically 8 bytes on 64-bit systems.

📝 Syntax

expert

Correct pointer declaration and initialization

Which option correctly declares and initializes a pointer to the first element of an integer array named 'data'?

A int ptr = &data[0];

B int ptr* = data;

C int *ptr = &data[0];

D int *ptr = data[0];

💡 Hint

Pointer must be declared with * and initialized with address of an element.

Option C correctly declares a pointer to int and initializes it with the address of the first element of the array.