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Different ways of String Reversal in C#

As you may be aware C#'s string class don’t have a Reverse() function by default, so let’s discuss different ways to reverse a given string:

Using manual reversal way:
The traditional way is to reverse a string by manually looping through it character by character and creating a new string.

string inputStr = "This is test string";
string outputStr = "";
for (int i = inputStr.Length - 1; i >= 0; i--)
{
    outputStr += inputStr[i];
}

One thing to remember though, if you are using this approach to reverse a large string then you should use StringBuilder to create output string instead of string because a string instance is immutable and you cannot change it after it was created. Any operation that appears to change the string instead returns a new instance.

Using Array.Reverse():
The second approach we can reverse a string is with the inbuilt Array.Reverse() method of Array class.

string inputStr = "This is test string";
char[] charArray = inputStr.ToCharArray();
Array.Reverse(charArray);

string outputStr = new string(charArray);

Here first of all we convert the given string to a character array and then we reverse that array using in-built method, and in last we construct a new string from the reversed array.

Reverse using LINQ:
LINQ allows us to shorten string reversal into a one line of code. In this scenario first of all the string is converted to a char array as in second approach. Array implements IEnumerable, so we can use LINQ's Reverse() method on it. After that with a call to ToArray() the resulting IEnumerable is then again converted to a character array, which is then used in the string constructor.

string inputStr = "This is test string";
string outputStr = new string(inputStr.ToCharArray().Reverse().ToArray());

Create extension method for reusability:
If we need string reversal on several places in our program or application, in such cases we can create an extension method on string and can use this wherever needed.

First of all create an extension method under class StringExtensions.

static class StringExtensions
{
    public static string ReverseString(this string inputStr)
    {
        return new string(inputStr.ToCharArray().Reverse().ToArray());
    }
}

Once extension method is ready to use then you can use it like any other string extension methods i.e. ToString(), ToUpper() etc.

string inputStr = "This is test string";
Console.WriteLine(inputStr.ReverseString());
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