public string reArrange(string s)
{
    char[] array = s.ToCharArray();
    int length = array.Length;
    char[] arranged = new char[length];

    for (int i = 0; i < length; i++)
    {
        int newposition = length - i;
        arranged[newposition] = array[i];
    }

    return new string(arranged);
}

int newposition = length - i - 1;

public static string Reverse( string s )
{
    char[] charArray = s.ToCharArray();
    Array.Reverse( charArray );
    return new string( charArray );
}

for (int i = 0; i < length-1; i++)

public string reArrange(string s)
{
    char[] array = s.ToCharArray();
    int length = array.Length;
    char[] arranged = new char[length];

    for (int i = 0; i < length; i++)
    {
       int newposition = length - i - 1;
       arranged[newposition] = array[i];
    }
    return new string(arranged);
}