[C language series] - realize the exchange of two numbers without creating the third variable

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Introduction to this article ： Realize the exchange of two numbers ！

Get to know the author ： Aspire to be a great programmer , Xiaobai, who is currently a sophomore in College .

Inspirational terms ： The tediousness of programming , Let's study together and become interesting ！

    Text begins

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List of articles

The opening

Hypothetical thinking

Add and subtract solution ideas

Exclusive or law

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The opening

The previous one came from （ Tea shares ） I believe you are not very unfamiliar with the written examination questions of , Here, let's recall the practice of this problem again ：
subject ： Two exchanges int The value of the variable , The third variable... Cannot be used , namely a=5,b=3, After the exchange a=5,b=3;
You are right , The title is so simple and clear , Is there a trap ？— I don't think so , But if you were a classmate in the written examination at that time , I guess you can't do it ！ Ha ~

Hypothetical thinking

Let's make a hypothesis here , Suppose there is no rule in the middle that it is not allowed to create the third variable （ Think like this , My rules are my rules ）
I think most of my classmates are like me , It's easy , There are no conditions , Directly write an exchange function , Completed this beautiful Exchange —so easy

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
void  Swap(int* x, int* y)// Implement this exchange function （ Accept with a pointer ）
{
	int tmp = 0;// Define an intermediate variable to exchange two values 
	tmp =*x;
	*x = *y;
	*y = tmp;
}
int main()
{
	int a = 5;// The variable value given by the topic 
	int b = 3;
	printf("exchange before a=%d b=%d\n", a, b);// Print the value before exchange 
	Swap(&a, &b);// Write a commutation function , take a,b Pass on your address （ Note that the value transfer cannot be changed main The value inside the function ）
	printf("exchange after a=%d b=%d\n", a, b);// Print the value after exchange 
	return 0;
}

Na , The running result you want ！
OK！ A small exchange function is done by us – Wait, don't you mean you can't create the third variable — Yeah
Next, let's follow - Here we try to add and subtract , Can we solve the problem

Add and subtract solution ideas

（1）： First the a And b The value of the sum of the additions is assigned to a
（2）： After the exchange b computing method ： Is to get the original a Well , Just subtract... From the sum of the additions b Just go , At this time b It is equal to that before the exchange a 了
（3）： After the exchange a computing method ： use （1） Add and subtract （2） Medium b, Just before the exchange b 了
Take an example ：

Is this clearer ！（ Stop talking nonsense , Write code quickly – forehead , good ！~） 

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int a = 5;
	int b = 3;
	printf("exchange before a=%d b=%d\n", a, b);// Print the value before exchange 
	a = a + b;
	b = a - b;
	a = a - b;
	printf("exchange after a=%d b=%d\n", a, b);// Print the value after exchange 
}

The result of running is the same ！

 Ok! The exchange was successful - Get it done （ what , You have to hand over a large number , And negative numbers , Sorry, I can't control so much code , Try to improve yourself ）
All right , Uncertain , Then I'll introduce you to another method ：

Exclusive or law

（1）: Have learned XOR （^） This operator
In fact, every number is composed of 32 individual bite Bits are combined
XOR is the use of bite position Same as 0, Dissimilarity is 1
（2）： It's no use saying more , Look at the train of thought ：
First of all, will a,b The value of XOR to a On ,
Want to get the exchange b： Just use XOR a And previous b Exclusive or , Just get the previous a 了 ,（ Similarly, this has to be exchanged a）
Tear your hands bite I'll show you ：

Have you understood the idea , Handwritten code on ：

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int a = 5;
	int b = 3;
	printf("exchange before a=%d b=%d\n", a, b);// Print the value before exchange 
	a = a ^ b;
	b = a ^ b;
	a = a ^ b;
	printf("exchange after a=%d b=%d\n", a, b);// Print the value after exchange 
	return 0;
}

  The running result is the same ~ Ok This is the real deal ！