Common array operations in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array sum using std::accumulate

What is the output of the following C++ code?

C++

#include <iostream>
#include <numeric>
#include <array>

int main() {
    std::array<int, 5> arr = {1, 2, 3, 4, 5};
    int sum = std::accumulate(arr.begin(), arr.end(), 0);
    std::cout << sum << std::endl;
    return 0;
}

A 15

B 10

C 0

D Compilation error

💡 Hint

std::accumulate adds all elements starting from the initial value.

The std::accumulate function sums all elements in the array starting from 0, so 1+2+3+4+5 = 15.

❓ Predict Output

intermediate

Output of array element access and modification

What is the output of this C++ code snippet?

C++

#include <iostream>
#include <array>

int main() {
    std::array<int, 3> arr = {10, 20, 30};
    arr[1] = arr[0] + arr[2];
    std::cout << arr[1] << std::endl;
    return 0;
}

A 40

B Runtime error

C 30

D 20

💡 Hint

arr[1] is assigned the sum of arr[0] and arr[2].

arr[0] is 10 and arr[2] is 30, so arr[1] becomes 40. The output is 40.

❓ Predict Output

advanced

Output of array reverse using std::reverse

What is the output of this C++ program?

C++

#include <iostream>
#include <array>
#include <algorithm>

int main() {
    std::array<int, 4> arr = {1, 2, 3, 4};
    std::reverse(arr.begin(), arr.end());
    for (int x : arr) {
        std::cout << x << " ";
    }
    return 0;
}

A 1 2 3 4

B Runtime error

C Compilation error

D 4 3 2 1

💡 Hint

std::reverse reverses the order of elements in the array.

The std::reverse function reverses the array elements, so the output is '4 3 2 1 '.

❓ Predict Output

advanced

Output of array fill and print

What does this C++ code print?

C++

#include <iostream>
#include <array>

int main() {
    std::array<int, 5> arr;
    arr.fill(7);
    for (auto val : arr) {
        std::cout << val << " ";
    }
    return 0;
}

A Compilation error

B 0 0 0 0 0

C 7 7 7 7 7

D Random values

💡 Hint

The fill() method sets all elements to the given value.

arr.fill(7) sets every element in the array to 7, so the output is '7 7 7 7 7 '.

🧠 Conceptual

expert

Behavior of std::array size and data pointers

Consider the following C++ code snippet. What is the output?

C++

#include <iostream>
#include <array>

int main() {
    std::array<int, 3> arr = {5, 10, 15};
    std::cout << arr.size() << " " << *(arr.data() + 1) << std::endl;
    return 0;
}

A 3 5

B 3 10

C Compilation error

D Runtime error

💡 Hint

arr.size() returns the number of elements; arr.data() returns pointer to first element.

arr.size() returns 3 because the array has 3 elements. arr.data() points to the first element (5), so *(arr.data() + 1) is the second element (10).