/* I have a O(len/2) method. I never worked in Delphi, so I'll post the code in C++ (2010 << I hope there's no problem >> ): */
#include <iostream>
using namespace std;

int main(void)
{
    char S[128], temp;
    cout << "Original string = "; cin.getline(S, sizeof(S));
    for(int i(0), j = strlen(S), k(j >> 1), x; i < k; ++i)
    {
        // Swap
        x = j - i - 1;
        S[i] ^= S[x];
        S[x] ^= S[i];
        S[i] ^= S[x];
    }
    cout << "Reverse string = " << S;
    system("pause>nul");
    return EXIT_SUCCESS;
}