C# – String versus StringBuilder

This is a frequent topic in a lot of interviews I have been a part of recently. A person would have to explain why you should use a StringBuilder instead of a String. If you can’t explain the difference, you probably need to beef up your C# knowledge. You are in luck today. I will show you why.

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace StringvsStringBuilder
{
  class Program
  {
    // This is the number of characters to be added
    static int NUM_OF_CHARACTERS = 25000;
 
    static void Main(string[] args)
    {
      string data1 = "";
 
      // Remember when we started for the String
      DateTime data1Start = DateTime.UtcNow;
 
      // Add a one to the existing string x times
      for (int i = 0; i < NUM_OF_CHARACTERS; i++)
      {
        data1 += "1";
      }
 
      // Remember when we ended for the String
      DateTime data1End = DateTime.UtcNow;
 
      StringBuilder data2 = new StringBuilder();
 
      // Remember when we started for the StringBuilder
      DateTime data2Start = DateTime.UtcNow;
 
      // Append a 1 x times to the StringBuilder
      for (int i = 0; i < NUM_OF_CHARACTERS; i++)
      {
        data2.Append("1");
      }
 
      // Remember when we ended for the StringBuilder
      DateTime data2End = DateTime.UtcNow;
 
      // Creating nice objects for the console output
      TimeSpan timeSpan1 = new TimeSpan(data1End.Ticks - data1Start.Ticks);
      TimeSpan timeSpan2 = new TimeSpan(data2End.Ticks - data2Start.Ticks);
 
      Console.WriteLine("String appending took {0:N0} milliseconds", timeSpan1.TotalMilliseconds);
      Console.WriteLine("StringBuilder appending took {0:N0} milliseconds", timeSpan2.TotalMilliseconds);
 
      // Check to see if the string and the toString of the StringBuilder are equal
      if(data1.Equals(data2.ToString())) {
        Console.WriteLine("Yes, the two strings are equal.");
      }
 
      Console.ReadKey();
    }
  }
}

The results on my system were:

String appending took 706 milliseconds

StringBuilder appending took 1 milliseconds

Yes, the two strings are equal.

Why should you use StringBuilder instead of String? If you are appending a lot of strings, StringBuilder is more efficient.