Swap two integers without using a third variable

Question

I have an assignment in which I need to swap two integers without using third variable. I'm not sure how to do this. How would I code this?

Try explaining it to us in a better way and maybe that will put you on the right track. — skyfoot, Apr 27 '12 at 11:54

score 19 · Answer 1 · answered Apr 27 '12 at 11:58

19

Yes, it's possible:

Dim var1 = 1
Dim var2 = 2
var1 = var1 + var2
var2 = var1 - var2
var1 = var1 - var2

But why do you need it? The code becomes abstruse.

answered Apr 27 '12 at 11:58

Tim Schmelter

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score 7 · Answer 2 · edited Sep 25 '12 at 19:13

7

Lets assume

a = 10; 
b = 20; 

a = a + b; // a = 30

b = a - b; // b = 10
a = a - b; // a = 20

Values swapped.

edited Sep 25 '12 at 19:13

sshannin

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answered Apr 27 '12 at 11:56

Paul Grimshaw

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score 5 · Answer 3 · answered Apr 27 '12 at 11:57

Read up on the "xor swap algorithm."

You can find an answer here:

http://www.java2s.com/Tutorial/VB/0040__Data-Type/Swaptwointegerswithoutusingathird.htm

firstValue = firstValue Xor secondValue
secondValue = firstValue Xor secondValue
firstValue = firstValue Xor secondValue

score 3 · Answer 4 · answered Apr 27 '12 at 12:04

3

 Dim a As Integer
 Dim b As Integer
 a= 1
 b= 2

 a = a Xor b
 b = a Xor b
 a = a Xor b

answered Apr 27 '12 at 12:04

Prashanth Thurairatnam

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Jainendra · Answer 5 · 2012-10-02T10:20:18.030

2

To swap two numeric variables do like this

a = a + b;
b = a - b;
a = a - b;

OR

a = a xor b;
b = a xor b;
a = a xor b;

where a and b are variables to be swapped

edited Oct 02 '12 at 10:20

answered Apr 27 '12 at 11:57

Jainendra

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To swap two *numeric* variables – Matt Wilko Apr 27 '12 at 12:26

score 1 · Answer 6 · answered Dec 18 '14 at 18:13

theoretically 3 ways

a = 4 , b = 5

1. Using XOR

a = a XOR b = 4 XOR 5 = 9     
b = a XOR b = 9 XOR 5 = 4
a = a XOR b = 9 XOR 4 = 5

2. Using +,-

a = a+b = 4+5 = 9     // should not overflow
b = a-b = 9-5 = 4
a = a-b = 9-4 = 5

3. Using *,/

a = a*b = 4*5 = 20    // should not overflow
b = a/b = 20/5 = 4    // should not overflow and should not be irrational number
a = a/b = 20/4 = 5    // should not overflow and should not be irrational number

score 0 · Answer 7 · answered Apr 27 '12 at 12:31

0

The Xor or a+b algorithms above work and are the best way to do this, but just an example of a weird way to do it. Still not sure why you would want to do this. Just build a function that you supply two values ByRef and have it do the standard swap method.

Dim newList as New List(Of Integer)
newList.Add firstvalue
newList.Add secondValue
newList.Reverse
secondValue = newList.Item(0)
firstValue = newList.Item(1)

answered Apr 27 '12 at 12:31

APrough

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Good idea, although `newList` might be considered as third variable. – Olivier Jacot-Descombes Sep 25 '12 at 19:08

score 0 · Answer 8 · answered Aug 06 '14 at 23:54

0

    Take two text boxes and a command box.In command box type this code.  
    text1.text=val(text1.text) + val(text2.text)      
    text2.text=val(text1.text) - val(text2.text)  
    text1.text=val(text1.text) - val(text2.text)

answered Aug 06 '14 at 23:54

ras123

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score 0 · Answer 9 · answered Feb 27 '16 at 03:07

Check link written for you

Approach#1.

Addition and Subtraction Method

Integer a, b
read a and b
a= a+b;
b=a-b;
a=a-b;

Problem:

Incorrect result when sum of numbers will exceed the Integer range.

Approach#2.

Multiplication and Division Method

Integer a, b
read a and b
a=a*b;
b=a/b;
a=a/b;

Problems:

If the value of a*b exceeds the range of integer.
If the value of a or b is zero then it will give wrong results.

Approach#3.

XOR Method

Integer a , b
read a and b
a=a^b;
b=a^b;
a=a^b;

Best approach to solve this problem without any pitfalls.

Swap two integers without using a third variable

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