Strings are a vital part of applications and building strings can take up a lot of time, along with also causing a performance lag in the applications. There are many ways in which you can build strings in C# programs. Consider this console application:

class Program
{
	static void Main(string[] args)
	{
		SomeStringBuildMethod("Max K. Smith", "36");

		Console.WriteLine("Done.");
		Console.ReadLine();
	}

	private static void SomeStringBuildMethod(string name, string age)
	{
		string str = string.Empty;

		// option #1
		str = "Name: " + name + ", Age: " + age;
		Console.WriteLine(str);

		// option #2
		str = string.Format("Name: {0}, Age: {1}", name, age);
		Console.WriteLine(str);

		// option #3 - best possibility before C# 6.0
		var builder = new StringBuilder();
		builder.Append("Name: ");
		builder.Append(name);
		builder.Append(", Age: ");
		builder.Append(age);
		str = builder.ToString();
		Console.WriteLine(str);

		// option #4 - best possibility C# 6.0+
		str = $"Name: {name}, Age: {age}";
		Console.WriteLine(str);
	}
}

Although many tend to option #1 this is by far the worst choice.

Strings in C# are immutable. This means that if you update their values, they are recreated and previous handles are removed from the memory. This is time consuming. Therefore bad.

String.Format in option #2 seems like a good choice but will be quite hard to mainten as soon as you've got more than a few parameters and need to add an additional one.

StringBuilder as used in option #3 was the best performance choice until the release of C# ver 6.0 - but yes, one has to type in much more code then in option #1.

The string interpolation operator $ introduced with C# 6.0 provides you with the facility of performing the string concatenation in best possible way, definitely killing options 1 and 2.

Under the hood, string interpolation uses String.Format - this brings a cleaner look to your programs when someone else is reading the code, along with increasing performance.

But for larger strings one will allways have to fallback to StringBuilder.