Reverser.cs

public static class Reverser
{
    public static string Reverse(string word)
    {
        // Create the stack
        var stack = new Stack<char>();
        
        // Insert each character from the string input in the stack
        foreach (var character in word)
        {
            stack.Push(character);
        }

        // Pop characters from the stack 
        // and store in a StringBuilder
        var builder = new StringBuilder();
        while (!stack.IsEmpty)
        {
            builder.Append(stack.Pop());
        }

        return builder.ToString();
    }
}