【日常练习】将两个数组的值进行交换；求分子为1正负交替分母加绝对值1的分数相加和；输出1~100之间数字末尾为9的数字

#include
#include
#include
#include
将数组a的内容和数组b的内容进行交换（数组一样大）
int main()
{
	int arr1[] = { 1,3,5,7,9 };
	int arr2[] = { 3,4,5,6,7 };
	int tmp;
	int i = 0;
	for (i = 0;i < sizeof(arr1) / sizeof(arr1[0]);i++)
	{
		tmp = arr1[i];
		arr1[i] = arr2[i];
		arr2[i] = tmp;
	}
	for (i =0 ;i < sizeof(arr1) / sizeof(arr1[0]);i++)
	{
		printf("%d ", arr1[i]);
	}
	printf("\n");
	for (i = 0;i < sizeof(arr1) / sizeof(arr1[0]);i++)
	{
		printf("%d ", arr2[i]);
	}
	system("pause");

	return 0;
}
main() {
	int i;	
	float sum = 0.0,temp = 0.0;
	for (i = 1;i <= 100;i++)
	{
		temp = pow(-1, i + 1);
		sum = sum + temp * 1 / i;
	}
	printf("sum is %f\n", sum);system("pause");return 0;
}
编写程序数一下1-100所有整数中出现多少次数字9
main() {
	int i;
	for (i = 1;i <= 100;i++) {
		if (i % 10 == 9) {
			printf("%d ", i);
		}
	}
	system("pause");
	return 0;
}