2022-04-15_for循环等_作业

编写程序数一下 1到 100 的所有整数中出现多少个数字9

#include <stdio.h>

int main()
{
	int count = 0;
	for (int i = 1; i <= 100; i++)
	{
		if (i % 10 == 9)
			count++;
		if (i / 10 == 9)
			count++;
	}
	printf("%d\n", count);

	return 0;
}

计算1/1-1/2+1/3-1/4+1/5 …… + 1/99 - 1/100 的值，打印出结果

#include <stdio.h>

int main()
{
	int i = 0;
	double sum = 0;
	int flag = 1;
	for (i = 1; i <= 100; i++)
	{
		sum = sum + (flag) * (1.0 / i);
		flag = -flag;
	}
	printf("%lf\n", sum);

	return 0;
}

求10 个整数中最大值

#include <stdio.h>

int main()
{
	int arr[10] = { 0,1,3,5,-1,2,7,8,4,-2 };
	int max = arr[0];
	for (int i = 1; i < 10; i++)
	{
		if (arr[i] > max)
			max = arr[i];
	}
	printf("%d\n", max);

	return 0;
}

在屏幕上输出9*9乘法口诀表

#include <stdio.h>

int main()
{
	for (int i = 1; i <= 9; i++)
	{
		for (int j = 1; j <= i; j++)
		{
			printf("%d*%d=%-2d ", j, i, j * i);
		}
		printf("\n");
	}

	return 0;
}

二分查找

编写代码在一个整形有序数组中查找具体的某个数
要求：找到了就打印数字所在的下标，找不到则输出：找不到。

#include <stdio.h>

int main()
{
	int arr[] = { 0,1,2,3,4,5,6,7,8,9 };
	int k = 0;
	scanf("%d", &k);
	int left = 1;
	int right = sizeof(arr) / sizeof(arr[0]);
	while (left <= right)
	{
		int mid = left + (right - left) / 2;
		if (k > arr[mid-1])
			left = mid + 1;
		else if (k < arr[mid-1])
			right = mid - 1;
		else
		{ 
			printf("找到了,下标: %d\n", mid-1);
			break;
		}
	}
	if (left > right)
		printf("找不到\n");
	return 0;
}