20200530test

//统计0-100 数字中9的总个数
#include
int main()
{
  int i = 0;
  int count = 0;
  for (i = 1; i <= 100; i++)
  {
    if (i % 10 == 9)
    {
      count++;
    }
    if (i /10 == 9)
    {
      count++;
    }
  }
  printf("count=%d\n", count);

  return 0;
}

//1-1/2+1/3-1/4+1/5...+1/99-1/100的值
int main()
{
  int i = 0;
  double sum = 0.0;
  int flag = 1;
  for (i = 1; i <= 100; i++)
  {
    sum += flag* 1.0 / i;
    flag= -flag;
  }
  printf("%lf\n", sum);
  return 0;
}

//10个数字中的最大值
int main()
{
  int i = 0;
  int arr[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
  int max = arr[0];
  int sz = sizeof(arr) / sizeof(arr[0]);
  for (i = 1; i <= 10; i++)
  {
    if (arr[i] > max)
    {
      max = arr[i];
    }
  }
  printf("max=%d\n", max);
  return 0;
}

//打印九九乘法表
#include
int main()
{
  int i = 0;
  for (i = 1; i <= 9; i++)
  {
    int j = 1;
    for (j = 1; j <= i; j++)
    {
      printf("%d*%d=%-2d ", i, j, i*j);
    }
    printf("\n");
  }
  return 0;
}

//猜数字游戏
#include 
#include 
#include 
void menu()
{
  printf("**********************************\n");
  printf("*********** 1.play     **********\n");
  printf("*********** 0.exit     **********\n");
  printf("**********************************\n");
}
//RAND_MAX--rand函数能返回随机数的最大值。
void game()
{
  int random_num = rand() % 100 + 1;
  int input = 0;
  while (1)
  {
    printf("请输入猜的数字>:");
    scanf("%d", &input);
    if (input > random_num)
    {
      printf("猜大了\n");
    }
    else if (input < random_num)
    {
      printf("猜小了\n");
    }
    else
    {
      printf("恭喜你，猜对了\n");
      break;
    }
  }
}
int main()
{
  int input = 0;
  srand((unsigned)time(NULL));
  do
  {
    menu();
    printf("请选择>:");
    scanf("%d", &input);
    switch (input)
    {
    case 1:
      game();
      break;
    case 0:
      break;
    default:
      printf("选择错误,请重新输入!\n");
      break;
    }
  } while (input);
  return 0;
}