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1, 将数组A中的内容和数组B中的内容进行交换。（数组一样大）

#include <stdio.h>
#include<stdlib.h>
int main()
     {
         int A[5] = { 1, 3, 5, 7, 9 };
	     int B[5] = { 2, 4, 6, 8, 10 };
	     int C[5] = { 0, 0 ,0 ,0 ,0};
	     for (int i = 0; i < 5; i++)
	{
		C[i] = A[i];
		A[i] = B[i];
		B[i] = C[i];
	     }
	    for (int i = 0; i < 5; i++)
	{
		printf("%d ", A[i]);
	    }
	    printf("\n");
		for (int i = 0; i < 5; i++)
	{
		printf("%d ", B[i]);
		}
		
		system("pause");
        }

2.计算1/1-1/2+1/3-1/4+1/5 …… + 1/99 - 1/100 的值。

#include<stdio.h>
#include<stdlib.h>
int main()
    in{
     int    a = 1;
	double sum = 1.0;
	double i;
	for (i = 2; i <= 100; i++)
	{
	a = (-1) * a;
	sum = sum + a / i;
	}
	printf("%f\n", sum);
	system("pause");
	return 0;
   }

编程写一下1~100的所有整数中出现多少次数字9

#include <stdio.h>
#include <stdlib.h>
int main()
{
  int i = 0;
  int a = 0 ;
  for(i = 1;i <= 100;i++)
  {
  if(i%10 == 9||i / 10 == 9)
  a++;
  }
  printf("%d\n",a);
  system("pause");
}