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C# | Swap two Strings without using third user defined variable

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Given two string variables a and b, swap these variables without using a temporary or third variable in C#. Use of library methods is allowed.


a = "Hello"
b = "World"

Strings before swap: a = Hello and b = World
Strings after swap: a = World and b = Hello

The idea is to do string concatenation and then use Substring() method to perform this operation. The Substring() method comes in two forms as listed below:

  • String.Substring Method (startIndex): This method is used to retrieve a substring from the current instance of the string. The parameter “startIndex” will specify the starting position of substring and then substring will continue to the end of the string.
  • String.Substring Method (int startIndex, int length): This method is used to extract a substring that begins from specified position described by parameter startIndex and has a specified length. If startIndex is equal to the length of string and parameter length is zero, then it will return nothing as substring.


1) Append second string to first string and 
   store in first string:
   a = a + b

2) Call the Substring Method (int startIndex, int length)
   by passing startindex as 0 and length as,
   a.Length - b.Length:
   b = Substring(0, a.Length - b.Length);

3) Call the Substring Method(int startIndex) by passing 
   startindex as b.Length as the argument to store the 
   value of initial b string in a
   a = Substring(b.Length);

// C# program to swap two strings
// without using a temporary variable.
using System;
class GFG {
    // Main Method
    public static void Main(String[] args)
        // Declare two strings
        String a = "Hello";
        String b = "Geeks";
        // Print String before swapping
        Console.WriteLine("Strings before swap: a ="
                          " " + a + " and b = " + b);
        // append 2nd string to 1st
        a = a + b;
        // store initial string a in string b
        b = a.Substring(0, a.Length - b.Length);
        // store initial string b in string a
        a = a.Substring(b.Length);
        // print String after swapping
        Console.WriteLine("Strings after swap: a =" +
                          " " + a + " and b = " + b);


Strings before swap: a = Hello and b = Geeks
Strings after swap: a = Geeks and b = Hello

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Last Updated : 18 Oct, 2021
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