ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

In computer programming, how do I Reverse a String?

Updated on September 4, 2015
Basketball, stored as a string with a zero-based index, is a collection of the individual characters.
Basketball, stored as a string with a zero-based index, is a collection of the individual characters.

What is a string?

In most programming languages, a string is simply an array of individual characters. This is common among all languages that support strings. The actual implementation differs between languages.

Some programming languages allow characters to be changed inside the string, while others do not. When a string can have its characters edited, it is called "mutable." When a string cannot have its characters edited, it is called "immutable." C++ allows the individual characters of a string to be edited, so it is mutable. C# does not allow the individual characters of a string to be edited, so it is immutable. Any edits to a string in C# results in the program allocating enough memory for the new string, and then creating the new string in that place.

Another thing to be aware of with your programming language of choice is how the environment indexes collections. Both C++ and C# will refer to the very first character as being in position 0. If a string had 10 characters, such as "Basketball", then the first character would be in position 0 and the final character in position 9. This is called "zero-based indexing." Other languages will refer to the first character as position 1, and the final character as position 10. This is called "one-based indexing." Visual Basic uses one-based indexing by default, but can be set to use zero-based indexing. SmallTalk and Lua both use one-based indexing as well.

How do I reverse a String? (Mutable)

Reversing a string is relatively simple and can be done in O(N) time, but the method is different depending on whether the string is mutable or immutable.

For a mutable string, characters can be swapped. Starting at the first character, swap the first and last character. Move to the second character. Swap the second and second-to-last character. Continue until you reach the halfway point in the string. Once all the swaps are completed, the string is reversed.

How to reverse a string with C++ (Mutable)

#include <iostream>
#include <string>

using namespace std;

void Reverse(string &str)
{
    char temp;
    uint length = str.length();
    
    for (uint x = 0; x < length / 2; x++)
    {
        if (x != length - 1 - x)
        {
            temp = str[length - 1 - x];
            str[length - 1 - x] = str[x];
            str[x] = temp;
        }
    }
}

int main()
{
    string input = "";
    
    cout << "Please enter any string: ";
    getline(cin, input);
    
    cout << "You entered: " << input << endl;
    
    Reverse(input);
    
    cout << "Input reversed: " << input << endl;
    
    return 0;
}

How do I reverse a String? (Immutable)

For an immutable string, you will have to build a new string. You cannot swap the characters in the original string. Create a new container, either a String or any other class that allows you to assemble a string, such as StringBuilder. From here, start at the final character in the original string, and add this character as the first to the new container. Keep moving over each character in the original string until you arrive at the first character. This addition will be the final character in the new string. Either return the new string from your method, or assign the value of the new string to the original string.

How to reverse a string with C# (Immutable)

using System;
using System.Text;

namespace StringReverse
{
    class Program
    {
        static void Reverse(ref string str)
        {
            StringBuilder rev = new StringBuilder();

            for (int x = str.Length - 1; x >= 0; x--)
            {
                rev.Append(str[x]);
            }

            str = rev.ToString();
        }

        public static void Main()
        {
            string input = "";

            Console.Write("Please enter any string: ");
            input = Console.ReadLine();

            Console.WriteLine("You entered: " + input);

            Reverse(ref input);

            Console.WriteLine("Input reversed: " + input);

            Console.Write("\nPlease press [ENTER] to exit...");
            Console.ReadLine();
        }
    }
}

How do I reverse a String by casting to an Array?

An alternate method supported by some languages is to cast the string as an array. This works with languages where the string data type is distinct from an array of characters and requires an explicit cast.

C# is one such language. First, explicitly cast the string to an array of characters (char data type). Then, use the Array.Reverse() method with your character array as the sole parameter. Finally, create a new string with the character array as the parameter, assigning the value to the old string reference. The original string is no longer referenced and will be garbage collected, while the new reversed string is the new value of the original reference.

How to reverse a string using an explicit cast to an array with C#

using System;
using System.Text;

namespace StringReverse
{
    class Program
    {
        static void Reverse(ref string str)
        {
            char[] strArray = str.ToCharArray();
            Array.Reverse(strArray);
            str = new String(strArray);
        }

        public static void Main()
        {
            string input = "";

            Console.Write("Please enter any string: ");
            input = Console.ReadLine();

            Console.WriteLine("You entered: " + input);

            Reverse(ref input);

            Console.WriteLine("Input reversed: " + input);

            Console.Write("\nPlease press [ENTER] to exit...");
            Console.ReadLine();
        }
    }
}
working

This website uses cookies

As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://corp.maven.io/privacy-policy

Show Details
Necessary
HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
LoginThis is necessary to sign in to the HubPages Service.
Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
AkismetThis is used to detect comment spam. (Privacy Policy)
HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
Features
Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
MavenThis supports the Maven widget and search functionality. (Privacy Policy)
Marketing
Google AdSenseThis is an ad network. (Privacy Policy)
Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
Index ExchangeThis is an ad network. (Privacy Policy)
SovrnThis is an ad network. (Privacy Policy)
Facebook AdsThis is an ad network. (Privacy Policy)
Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
AppNexusThis is an ad network. (Privacy Policy)
OpenxThis is an ad network. (Privacy Policy)
Rubicon ProjectThis is an ad network. (Privacy Policy)
TripleLiftThis is an ad network. (Privacy Policy)
Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
Statistics
Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
ClickscoThis is a data management platform studying reader behavior (Privacy Policy)