1.计算n的阶乘

用for比较好

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	int i = 1;
	int n = 0;
	int sum = 1;
	scanf("%d", &n);
	for (i = 1;i <= n;i++)
	{ 
		sum *= i;
	}
	printf("%d\n", sum);
	return 0;
}

2.计算1！+2！+3！+……+10！

笨方法：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	int i = 0;
	int n = 0;
	int sum1 = 1;
	int sum2 = 0;
	for (n = 1;n <= 10; n++)
	{
		sum1 = 1;//每次开始前都要初始为1
		for (i = 1;i <= n; i++)
		{
			sum1 *= i;
		}
		sum2 += sum1;
	}	
		printf("%d\n", sum2);
	return 0;
}

改进：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	int i = 0;
	int n = 0;
	int sum1 = 1;
	int sum2 = 0;
	for (n = 1; n <= 10; n++)
	{
		sum1 *= n;
		sum2 += sum1;
	}
	printf("%d\n", sum2);
	return 0;
}

3.在一个有序数组中查找一个数字n

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
	int arr[] = { 1,2,3,4,5,6,7,8,9,10 };
	int k = 7;
	//在arr找7
	int sz = sizeof(arr) / sizeof(arr[0]);//计算一个元素的大小
	int left = 0;
	int right = sz - 1;
	while (left <= right)
	{
		int mid = (left + right) / 2;
		if (arr[mid] < k)
		{
			left = mid + 1;
		}
		else if (arr[mid] > k)
		{
			right = mid - 1;
		}
		else
		{
			printf("找到了，下表是：%d\n", mid);
			break;
		}
		if (left > right)
		{
			printf("找不到了\n");
		}
	}
	return 0;
}