cppintermediate10 minutes

Predict the Output: Array Transformation and Loop Logic in C++

Analyze the given C++ code snippet that performs multiple array transformations and loop operations. Predict the final output printed by the program without running it.

Challenge prompt

Consider the following C++ code: int arr[] = {2, 4, 6, 8}; int n = 4; for (int i = 0; i < n; i++) { arr[i] = arr[i] + i; } for (int i = n - 1; i > 0; i--) { arr[i] = arr[i] - arr[i - 1]; } for (int i = 0; i < n; i++) { std::cout << arr[i] << " "; } What is the output of this program when executed? Explain your reasoning.

Guidance

• Step through each loop iteration carefully, tracking how the array elements change.
• Remember the effect of modifying array elements in place and how that influences subsequent calculations.

Hints

• After the first loop, the array elements are incremented by their index positions.
• In the second loop, each element is updated based on the difference with the previous element, starting from the end.

Starter code

int arr[] = {2, 4, 6, 8};
int n = 4;

for (int i = 0; i < n; i++) {
    arr[i] = arr[i] + i;
}

for (int i = n - 1; i > 0; i--) {
    arr[i] = arr[i] - arr[i - 1];
}

for (int i = 0; i < n; i++) {
    std::cout << arr[i] << " ";
}

Expected output

2 2 0 2

Core concepts

array manipulationfor loopsin-place modificationbasic arithmetic operations

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