Reverse an Array in C

Arrays

Reverse an array in place by swapping pairs from opposite ends.

Complete program

#include <stdio.h>

int main(void) {
    int values[] = {1, 2, 3, 4, 5};
    size_t count = sizeof values / sizeof values[0];
    for (size_t i = 0; i < count / 2; ++i) {
        int temporary = values[i];
        values[i] = values[count - 1 - i];
        values[count - 1 - i] = temporary;
    }
    for (size_t i = 0; i < count; ++i)
        printf("%d%s", values[i], i + 1 == count ? "\n" : " ");
    return 0;
}

Try in Circuit →

Opens a new program without replacing your saved code. Press Run when you are ready.

How it works

Every pair needs exactly one swap. Iterating only to count / 2 prevents swapping elements back to their original positions. For an odd count, the middle element stays in place.

A temporary variable prevents losing the left-hand value when it is replaced. Test arrays with one, two, and four elements, then compare this algorithm with printing the original array backwards without changing it.

Expected output

5 4 3 2 1

Concepts to practice

• In-place algorithms
• Symmetric indexes
• Swapping

Predict a different input or change one value, then compare the result with your prediction. Keep changes within the documented bounds and read warnings before trusting an answer.