A string is a sequence of characters used to store text. It is a reference type in C# and is stored in heap memory. Strings are immutable, meaning that once they are created, they don’t change. This feature ensures that strings are thread-safe and easy to use.

We can combine two or more strings using the + operator, and they support various methods for manipulation and searching within them. We can also access individual characters using indexes, similar to an array of characters. C# provides escape sequences to represent special characters in strings.

Since strings are immutable, any modification results in a new string, rather than modifying the existing value. Hence, we need to be cautious while manipulating strings, as attempting to concatenate or modify a large number of strings can lead to performance and memory issues.

What exactly is a StringBuilder?

We can use StringBuilder when we need to make a lot of modifications to a string. StringBuilder is mutable, meaning we can change it without creating new strings. This helps save memory and boosts performance. We can efficiently add, replace, or delete parts of the string.

How StringBuilder works internally in C#

When we try to concatenate a string, it creates a new string due to the immutable nature of strings. On the other hand, StringBuilder internally uses a resizable buffer to store the characters of the string being constructed or modified.

This buffer is initially allocated with a specific capacity, and as the string grows, StringBuilder dynamically reallocates and expands the buffer to fit the added characters. This resizing process allows StringBuilder to efficiently manage memory while minimizing the overhead of constantly creating new string instances.

class Program
{
    static void Main(string[] args)
    {
        // String Concatenation
        string concatenated = "";
        for (int i = 65; i <= 90; i++)
        {
            // new string is created each time + is used
            concatenated += " " + (char)i;
        }
        Console.WriteLine($"String Concatenation Result: {concatenated}");
        
        // StringBuilder
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 65; i <= 90; i++)
        {
            // append adjusts the stringbuilder buffer size
            stringBuilder.Append(" ").Append((char)i);
        }

        string stringBuilderResult = stringBuilder.ToString();
        Console.WriteLine($"StringBuilder Result: {stringBuilderResult}");
    }
}