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How to reverse a string sentence (only words, not characters) without using the C# "string built-in" functions

, 5 Jan 2013 CPOL 27.1K 3
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Reverse of a string sentence


This article represents one of few ways of reversal of string sentence (only words, without using any inbuilt c# functions except String.Length property as author feels lazy to write code for it.)


Knowledge of control structures (for, foreach, while) and data types (char, string).

Using the code

There are mainly three functions created :

  1. ReverseString( String ): returns reversed string, e.g., ReverseString("Hello How are you").
  2. Split( String ): returns a string array containing words and spaces at consecutive places.
  3. ReturnSpace( int ): accepts an integer representing number of spaces, creates and return a string containing specified number of spaces.
/**Reverse a Sentence without using C# inbuilt functions
 (except String.Length property, m not going to write code for this small functionality )*/
const char EMPTYCHAR = ' ';
const string EMPTYSTRING = " ";

/// <summary>
/// Reverse a string Sentence
/// </summary>
/// <param name="pStr"></param>
/// <returns></returns>
public string ReverseString(string pStr)
  if (pStr.Length > 1) //can be checked/restricted via validation
    string strReversed = String.Empty;
    string[] strSplitted = new String[pStr.Length];
    int i;

    strSplitted = Split(pStr); // Complexity till here O(n)

    for (i = strSplitted.Length - 1; i >= 0; i--)
    // this for loop add O(length of string) in O(n) which is similar to O(n)
        strReversed += strSplitted[i];

    return strReversed;
  return pStr;

/// <summary>
/// Split the string into words & empty spaces
/// </summary>
/// <param name="str"></param>
/// <returns></returns>
public string[] Split(string str)
    string strTemp = string.Empty;
    string[] strArryWithValues = new String[str.Length];
    int j = 0;
    int countSpace = 0;

    //Complexity of for conditions result to O(n)
    foreach (char ch in str)
        if (!ch.Equals(EMPTYCHAR))
            strTemp += ch; //append characters to strTemp

            if (countSpace > 0)
                strArryWithValues[j] = ReturnSpace(countSpace); // Insert String with Spaces
                countSpace = 0;

            if (countSpace == 1)
                strArryWithValues[j] = strTemp; // Insert String with Words
                strTemp = String.Empty;

    strArryWithValues[j] = strTemp;
    return (strArryWithValues);

/// <summary>
/// Return a string with number of spaces(passed as argument)
/// </summary>
/// <param name="count"></param>
/// <returns></returns>
public string ReturnSpace(int count)
    string strSpaces = String.Empty;

    while (count > 0)
        strSpaces += EMPTYSTRING;

    return strSpaces;


/************Reverse Sentence Ends***************/

Similar post

Points of Interest

Maintaining complexity to O(n) where n is length of string.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Software Developer
United States United States
Learning & Earning.

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Comments and Discussions

SuggestionAnother suggestion Pin
Malte Klena9-Jan-13 7:08
memberMalte Klena9-Jan-13 7:08 
SuggestionHow about this... Pin
Andreas Gieriet5-Jan-13 12:11
memberAndreas Gieriet5-Jan-13 12:11 
QuestionRepeat Pin
jfriedman4-Jan-13 4:15
memberjfriedman4-Jan-13 4:15 
AnswerRe: Repeat Pin
PIEBALDconsult4-Jan-13 4:35
memberPIEBALDconsult4-Jan-13 4:35 
GeneralRe: Repeat Pin
jfriedman4-Jan-13 5:21
memberjfriedman4-Jan-13 5:21 
GeneralRe: Repeat Pin
PIEBALDconsult4-Jan-13 10:51
memberPIEBALDconsult4-Jan-13 10:51 
GeneralRe: Repeat Pin
VeeQuest5-Jan-13 9:24
memberVeeQuest5-Jan-13 9:24 
SuggestionUse StringBuilders Pin
John Brett2-Jan-13 22:06
memberJohn Brett2-Jan-13 22:06 
GeneralRe: Use StringBuilders Pin
adriancs3-Jan-13 7:46
memberadriancs3-Jan-13 7:46 
GeneralThoughts Pin
PIEBALDconsult2-Jan-13 16:38
memberPIEBALDconsult2-Jan-13 16:38 
Why not just use an appropriate constructor for string, I don't think it would violate the spirit of "not using built-in functions". Bear in mind that even the += operator is actually just shorthand for a "built-in function" anyway.
QuestionGood one Pin
maq_rohit2-Jan-13 14:53
membermaq_rohit2-Jan-13 14:53 
AnswerRe: Good one Pin
VeeQuest5-Jan-13 9:26
memberVeeQuest5-Jan-13 9:26 
GeneralRe: Good one Pin
maq_rohit9-Jan-13 19:28
membermaq_rohit9-Jan-13 19:28 

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