Swap two numbers without using another variable

Question

Swap two variables without using a temp variable if

int a=4; 
int b=3;

I need to swap these variable and get output as a=3 and b=4 without using another variable in C#

Any particular reason? I would have thought 3 MSIL **assignments** (`t = a; a=b; b=t; )` to be faster than **3 MSIL operations** followed by **3 assignments** judging by the answers below? — , Jan 29 '15 at 05:00
@MickyDuncan The speed is completely irrelevant here. There is no way anyone could have sat down to optimize their code and discovered the bottleneck was an extra statement when swapping two values. — Asad Saeeduddin, Jan 29 '15 at 05:03
@Asad So is arguably wanting to swap two variables without impacting the heap. This question represents questionable benefit — , Jan 29 '15 at 05:06
@EsotericScreenName Thanks. Yes for `floating-point` it is quite important. — , Jan 29 '15 at 05:19
**paxdiablo's** answer [here](http://stackoverflow.com/questions/804706/swap-two-variables-without-using-a-temp-variable) makes a good point. _"developers who try to use tricks to, for example, swap variables without using a temp or 'Duff's device' are just trying to show how clever they are"_. — , Jan 29 '15 at 14:24

score 7 · Answer 1 · 2015-01-29T05:22:51.373

7

Use Interlocked.Exchange()

int a = 4;
int b = 3;

b = Interlocked.Exchange(ref a, b);

Tell me more

From MSDN:

Sets a 32-bit signed integer to a specified value as an atomic operation, and then returns the original value

EDIT: Regarding Esoteric's fine link above (thank-you), there's even a Interlocked.Exchange() for double that may help there too.

edited Jan 29 '15 at 05:22

answered Jan 29 '15 at 05:15

score 5 · Accepted Answer · answered Jan 29 '15 at 04:49

5

use the following concept

int a=4 ;
int b=3 ;

a=a+b ;  //  a=7
b=a-b ;  //  b=7-3=4
a=a-b ;  //  c=7-4=3

answered Jan 29 '15 at 04:49

AcAnanth

score 3 · Answer 3 · answered Jan 29 '15 at 04:46

3

There are actually a couple of ways.

The following is considered an obfuscated swap.

a ^= b;
b ^= a;
a ^= b;

answered Jan 29 '15 at 04:46

Jonathan Wood

score 1 · Answer 4 · answered Jan 29 '15 at 04:46

1

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

Works the same with any language.

answered Jan 29 '15 at 04:46

Brad Christie

score 1 · Answer 5 · answered Jan 29 '15 at 04:48

1

Using addition and subtraction

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

Using xor operator

a = a ^ b;
b = a ^ b;
a = a ^ b;

answered Jan 29 '15 at 04:48

mmaynar1