方法一

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
  int a = 4;
  int b = 5;
  int temp = 0;
  temp = a;
  a = b;
  b = temp;
  printf("a=%d b=%d\n", a, b);//借助temp变量
return 0;
}

方法二

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
  int a = 4;
  int b = 5;

  a = a + b;//9
  b = a - b;//4
  a = a - b;//5

  printf("a=%d b=%d\n", a, b);//加减法
return 0;
}

方法三

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
  int a = 4;//...0100
  int b = 5;//...0101

  a = a ^ b;//...0001
  b = a ^ b;//...0100
  a = a ^ b;//...0101
  printf("a=%d b=%d\n", a, b);//应用a^b^b==a,异或
return 0;
}