Swap two numbers without using another variable [duplicate]

Question

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Swap two variables without using a temporary variable (30 answers)

Closed 10 years ago.

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#

• user585968: 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?
• user1726343: @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.
• user585968: @Asad So is arguably wanting to swap two variables without impacting the heap. This question represents questionable benefit
• Esoteric Screen Name: @MickyDuncan This is a rather typical interview question.
• user585968: @EsotericScreenName Thanks. Yes for floating-point it is quite important.

Answer 1

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.

Answer 2

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

Answer 3

There are actually a couple of ways.

The following is considered an obfuscated swap.

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

Answer 4

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

Works the same with any language.

• leppie: Just watch out for overflow :p

Answer 5

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;

http://chris-taylor.github.io/blog/2013/02/25/xor-trick/