Append('A ').Append('B ').Append('C... ') : StringBuilder « String « C# / CSharp Tutorial

1. C# / CSharp Tutorial
2. String
3. StringBuilder

using System;
using System.Text;

public class MainClass
{
    static void Main() {
        StringBuilder sb = new StringBuilder();

        sb.Append("A ").Append("B ").Append("C... ");

        string built1 = sb.ToString();

        sb.Append("D");

        string built2 = sb.ToString();

        Console.WriteLine( built1 );
        Console.WriteLine( built2 );
    }
}

A B C...
A B C... D