【C语言】指针的进阶（二）—— 回调函数的讲解以及qsort函数的使用方式

int Add(int x, int y)
{
  return x + y;
}
int Sub(int x, int y)
{
  return x - y;
}
int main()
{
  int (*pf1)(int, int) = &Add;  //pf1和pf2是函数指针
  int (*pf2)(int, int) = ⋐
  //数组中存放类型相同的多个数组
  int (*pfArr[4])(int, int) = { &Add,&Sub };  //pfArr就是函数指针数组
  return 0;
}

int add(int a, int b)
{
  return a + b;
}
int sub(int a, int b)
{
  return a - b;
}
int mul(int a, int b)
{
  return a * b;
}
int div(int a, int b)
{
  return a / b;
}
void menu()
{
  printf("*******************************\n");
  printf("******   1.add   2.sub    *****\n");
  printf("******   3.mul   4.div    *****\n");
  printf("******   0.exit           *****\n");
  printf("*******************************\n");
}
int main()
{
  int input = 0;
  int a = 0;
  int b = 0;
  int ret = 0;
  do
  {
    menu();
    printf("请选择:>");
    scanf("%d", &input);
    switch (input)
    {
    case 1:
      printf("请输入2个操作数:");
      scanf("%d %d", &a, &b);
      ret = add(a, b);
      printf("%d\n", ret);
      break;
    case 2:
      printf("请输入2个操作数:");
      scanf("%d %d", &a, &b);
      ret = sub(a, b);
      printf("%d\n", ret);
      break;
    case 3:
      printf("请输入2个操作数:");
      scanf("%d %d", &a, &b);
      ret = mul(a, b);
      printf("%d\n", ret);
      break;
    case 4:
      printf("请输入2个操作数:");
      scanf("%d %d", &a, &b);
      ret = div(a, b);
      printf("%d\n", ret);
      break;
    case 0:
      printf("退出计算器\n");
      break;
    default:
      printf("选择错误，重新选择\n");
      break;
    }
  } while (input);
  return 0;
}

int add(int a, int b)
{
  return a + b;
}
int sub(int a, int b)
{
  return a - b;
}
int mul(int a, int b)
{
  return a * b;
}
int div(int a, int b)
{
  return a / b;
}
void menu()
{
  printf("*******************************\n");
  printf("******   1.add   2.sub    *****\n");
  printf("******   3.mul   4.div    *****\n");
  printf("******   0.exit           *****\n");
  printf("*******************************\n");
}
int main()
{
  int input = 0;
  int a = 0;
  int b = 0;
  int ret = 0;
  do
  {
    menu();
    printf("请选择:>");
    scanf("%d", &input);
    //创建一个函数指针数组
    int (*pfArr[])(int, int) = { NULL,add,sub,mul,div };
                //为了使数组下标与菜单序号对应起来，在0下标处放置一个NULL
    if (input == 0)
    {
      printf("退出计算器\n");
    }
    else if (input >= 1 && input <= 4)
    {
      printf("请输入2个操作数:");
      scanf("%d %d", &a, &b);
      ret = pfArr[input](a, b); //下标访问数组中的函数并调用
      printf("ret = %d\n", ret);
    }
    else
    {
      printf("选择错误，重新选择\n");
    }
  } while (input);
  return 0;
}

void test(const char* str)
{
  printf("%s\n", str);
}
int main()
{
  //函数指针pfun
  void (*pfun)(const char*) = test;
  //函数指针的数组pfunArr
  void (*pfunArr[5])(const char* str);
  pfunArr[0] = test;
  //指向函数指针数组pfunArr的指针ppfunArr
  void (*(*ppfunArr)[5])(const char*) = &pfunArr;
  return 0;
}

int add(int a, int b)
{
  return a + b;
}
int sub(int a, int b)
{
  return a - b;
}
int mul(int a, int b)
{
  return a * b;
}
int div(int a, int b)
{
  return a / b;
}
void menu()
{
  printf("*******************************\n");
  printf("******   1.add   2.sub    *****\n");
  printf("******   3.mul   4.div    *****\n");
  printf("******   0.exit           *****\n");
  printf("*******************************\n");
}
void calc(int(*pf)(int, int))
{
  int a = 0;
  int b = 0;
  int ret = 0;
  printf("请输入2个操作数:");
  scanf("%d %d", &a, &b);
  ret = pf(a, b);
  printf("%d\n", ret);
}
int main()
{
  int input = 0;
  do
  {
    menu();
    printf("请选择:>");
    scanf("%d", &input);
    switch (input)
    {
    case 1:
      calc(add);
      break;
    case 2:
      calc(sub);
      break;
    case 3:
      calc(mul);
      break;
    case 4:
      calc(div);
      break;
    case 0:
      printf("退出计算器\n");
      break;
    default:
      printf("选择错误，重新选择\n");
      break;
    }
  } while (input);
  return 0;
}

//冒泡排序算法
//给一组整型数据，然后使用冒泡排序对数据进行升序排序。
void bubble_sort(int arr[], int sz)
{
  //趟数
  int i = 0;
  for ( i = 0; i < sz - 1; i++)
  {
    //每一趟冒泡排序的过程
    int j = 0;
    for ( j = 0; j < sz - 1 - i; j++)
    {
      if (arr[j] > arr[j + 1])
      {
        int tmp = arr[j];
        arr[j] = arr[j + 1];
        arr[j + 1] = tmp;
      }
    }
  }
}
int main()
{
  int arr[] = { 10,9,8,7,6,5,4,3,2,1 };
  int sz = sizeof(arr) / sizeof(arr[0]);
  bubble_sort(arr, sz);
  int i = 0;
  for ( i = 0; i < sz; i++)
  {
    printf("%d ", arr[i]);
  }
  return 0;
}

int cmp_int(const void* e1, const void* e2)
{
  return *(int*)e1 - *(int*)e2;
}

int cmp_int(const void* e1, const void* e2)
{
  return *(int*)e1 - *(int*)e2;
}
int main()
{
  int arr[] = { 10,9,8,7,6,5,4,3,2,1 };
  int sz = sizeof(arr) / sizeof(arr[0]);
  qsort(arr, sz, sizeof(arr[0]), cmp_int);
  int i = 0;
  for ( i = 0; i < sz; i++)
  {
    printf("%d ", arr[i]);
  }
  return 0;
}

struct Stu
{
  char name[20];
  int age;
};
int cmp_struct(const void* e1, const void* e2)
{
  return ((struct Stu*)e1)->age - ((struct Stu*)e2)->age;
}
int main()
{
  struct Stu arr[] = { {"zhangsan",20},{"lisi",21},{"wangwu",22} };
  int sz = sizeof(arr) / sizeof(arr[0]);
  qsort(arr, sz, sizeof(arr[0]), cmp_struct);
  return 0;
}