#define _CRT_SECURE_NO_WARNINGS 
#include<stdio.h>
int main()
{
  int n = 0;
  int i = 0;
  int ret = 1;
  printf("请输入n的值,来计算n的阶乘\n");
  scanf("%d", &n);//放不下了就溢出了，结果为0
  if (n == 0)
  {
  printf("n=0时，n的阶层为0\n");
  }
  else
  {
  for ( i = 1;i<=n;i++)
  { 
    ret = ret*i;
  }
  printf("n的阶乘=%d", ret);
  
  }
}
//for循环计算阶乘



#define _CRT_SECURE_NO_WARNINGS 
#include<stdio.h>
int main()
{
  int n = 0;
  int i = 0;
  int ret = 1;
  int sum = 0;
  for (n = 1; n <= 10;n++)
  {
  ret = ret*n;
  sum = sum + ret;
}
  printf("%d", sum);  
}
// 打印     1!+2!+3!+....+10！=？     4037913




#define _CRT_SECURE_NO_WARNINGS  
#include<stdio.h>

int main()

{

  int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

  int k = 11;

  int i = 0;

  int sz = sizeof(arr) / sizeof(arr[0]);

  for (i = 0; i < sz; i++)

  {

  if (k == arr[i])

  {

    printf("找到了，下标是%d\n", i);

    break;

  }

  }

  if (i == sz)

  printf("找不到\n");

  return 0;

}

// 寻找数组下标（低效，没有使用二分法）



#define _CRT_SECURE_NO_WARNINGS  
#include<stdio.h>

int main()

{

  int k = 11;

  int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

  int sz = sizeof(arr) / sizeof(arr[0]);//元素个数

  int left = 0;//左下标

  int right = 9;//右下标

  while (left <= right)

  {


  int mid = (left + right) / 2;

  if (arr[mid] > k)

  {

    right = mid - 1;

  }

  else if (arr[mid] < k)

  {

    left = mid + 1;

  }

  else

  {

    printf("找到了，下标是%d\n", mid);//当目标数字==k时

    break;                              //这个过程中mid就是对应数字的下标。

  }

 

  }//while 代码块下面部分
  
 if (left>right)

  {

    printf("找不到了\n");

  }
  return 0;

}

//寻找下标。如果找得到，显示下标；找不到，结果就是找不到了



//任务：逐渐显出 weicome to bit!!!!!!!，####################从两边向中间渐变。

#define _CRT_SECURE_NO_WARNINGS  
#include<stdio.h>

#include<windows.h>

#include<stdlib.h>


int main()

{

  char arr1[] = "welcome to bit !!!!!!!";

  char arr2[] = "######################";

  int left = 0;

  int right = sizeof(arr1) / sizeof(arr1[0]) - 2;

  //  strlen(arr1)-1;也行,需 #include<string.h>

  while (left <= right)

  {

  arr2[left] = arr1[left];

  arr2[right] = arr1[right];

        printf("%s\n", arr2);

  Sleep(200);

  system("cls");//执行系统命令的一个函数：cls-清空屏幕。

  left++;

  right--;

  }

  return 0;

}




//任务：登录 输入密码，最多错3次。3次以内，对了，就成功

#define _CRT_SECURE_NO_WARNINGS  
#include<stdio.h>

#include<windows.h>

#include<stdlib.h>




int main()

{

  int i = 0;

  char password[] = { 0 };

  for (i = 0; i <3; i++)

  {

  printf("请输入密码:>");

  scanf("%s", password);

  if (strcmp(password, "123456")==0)

  {

    printf("登陆成功\n");

    break;

  }

  else

  {

    printf("密码错误，请重试\n");

  }

  

  }

  if (i == 3);

  printf("三次密码均错误，请退出程序");


  
  return 0;

}