cppintermediate10 minutes

Predict the Output: Multi-dimensional Array and Pointer Arithmetic in C++

Analyze the provided C++ code snippet involving multi-dimensional arrays and pointer arithmetic. Predict the output without running the code.

Challenge prompt

Consider the following C++ code snippet: int main() { int arr[2][3] = {{1, 2, 3}, {4, 5, 6}}; int *ptr = &arr[0][0]; std::cout << *(ptr + 4) << " "; std::cout << *(*(arr + 1) + 1) << " "; std::cout << arr[1][2] << " "; std::cout << *(arr[0] + 2) << std::endl; return 0; } What will be the output of this code?

Guidance

• Remember how multi-dimensional arrays are laid out contiguously in memory in row-major order.
• Understand pointer arithmetic and how incrementing an int pointer moves it to the next integer element.

Hints

• The expression *(ptr + 4) accesses the 5th element from the beginning of the array.
• The expression *(*(arr + 1) + 1) accesses the element in the second row, second column.

Starter code

int main() {
    int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
    int *ptr = &arr[0][0];
    
    std::cout << *(ptr + 4) << " ";
    std::cout << *(*(arr + 1) + 1) << " ";
    std::cout << arr[1][2] << " ";
    std::cout << *(arr[0] + 2) << std::endl;
    
    return 0;
}

Expected output

5 5 6 3

Core concepts

pointer arithmeticmulti-dimensional arrays

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