Use the Insert() method to insert strings into StringBuilder : StringBuilder « String « C# / CSharp Tutorial

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

using System;
using System.Text;

class MainClass
{
  public static void Main()
  {
    StringBuilder myStringBuilder = new StringBuilder();
    myStringBuilder.Append("friends");
    
    myStringBuilder.Insert(2, "friends, ");
    myStringBuilder.Insert(2, "Romans, ", 3);
    Console.WriteLine("myStringBuilder = " + myStringBuilder);

  }
}