Reverse an Array Using Only Pointers

Code

#include <stdio.h>

void reverse_array(int *ptr, int n) {
    // Your logic here
    // for (int i = 0; i < n/2; i++)
    // {
    //     *(ptr + i) = *(ptr + i) ^ *(ptr + n - 1 -  i);
    //     *(ptr + n - 1 -  i) = *(ptr + i) ^ *(ptr + n - 1 -  i);
    //     *(ptr + i) = *(ptr + i) ^ *(ptr + n - 1 -  i);
    // }

    int *start = ptr;
    int *end = ptr + n - 1;
    
    while (start < end) {
        int temp = *start;
        *start = *end;
        *end = temp;
        
        start++;
        end--;
    }
    
}

int main() {
    int n;
    scanf("%d", &n);

    int arr[100];
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    reverse_array(arr, n);

    for (int i = 0; i < n; i++) {
        printf("%d", arr[i]);
        if(i < n-1){
            printf(" ");
        }
    }

    return 0;
}

Solving Approach

This version uses a temporary variable (`int temp`) to swap values
at the start and end of the array while iterating inward.

Reason for Choosing Temp Swap Over XOR Swap:
---------------------------------------------
✔️ Performance:
   - Temp swap: 2 memory reads + 2 writes per iteration
   - XOR swap: 3 reads + 3 writes (more CPU cycles)
   - Temp swap generates simpler machine code, better pipelining

✔️ Safety:
   - XOR swap has undefined behavior if start == end (middle of odd-sized array)
   - Temp swap is safe in all cases, even with overlapping pointers

✔️ Compiler Optimization:
   - Temp swap is easy to optimize into register operations
   - XOR-based logic may not get the same level of optimization

✔️ Readability and Maintainability:
   - Temp swap is easier to understand and modify
   - XOR logic is obscure and error-prone

✔️ Memory Use:
   - Temp swap uses 4 bytes extra (on stack) — negligible even in constrained environments
   - Operates in-place, no dynamic allocation