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=== Указатель на функцию ===

<code c++>
// Programming 1. Sample at 2017-03-02-13-55.55
#include <stdio.h>

struct Person
{
  const char *name;
  int age;
} person;

void print_nice(const struct Person *p)
{
  printf("Person %s age %d\n",p->name,p->age);
}

void print_ugly(const struct Person *p)
{
  printf("[%s,%d]\n",p->name,p->age);
}

void print(const struct Person *obj, 
  void (*printer)(const struct Person*))
{
  printer(obj);
}

int main(/*int c, char **v */)
{
  person.name = "Vasya";
  person.age = 15;

  print(&person,print_nice);
  print(&person,print_ugly);

  return 0;
}
</code>

=== Полиморфный принтер ===

<code c++>
// Programming 1. Sample at 2017-03-02-13-55.55
#include <stdio.h>

struct Person
{
  const char *name;
  int age;
  void (*print)(const struct Person*);
  void (*printer)(const struct Person*);
} person1, person2;

void print_nice(const struct Person *p)
{
  printf("Person %s age %d\n",p->name,p->age);
}

void print_ugly(const struct Person *p)
{
  printf("[%s,%d]\n",p->name,p->age);
}

void print(const struct Person *obj)
{
  obj->printer(obj);
}



int main(/*int c, char **v */)
{
  person1.name = "Vasya";
  person1.age = 15;
  person1.print = print;
  person1.printer = print_nice;

  person2.name = "Petya";
  person2.age = 51;
  person2.print = print;
  person2.printer = print_ugly;

  person1.print(&person1);
  person2.print(&person2);
  
  return 0;
}

</code>

=== Universal search ===
<code c++>
// Programming 1. Sample at 2018-02-15-14-55.05
#include <stdio.h>

struct S{
  int a;
  int b;
};

void* search( void *key,
              void *arr,
              int n,
              int size,
              int (*comp)(const void *, const void *)
            ){

  for(int i=0;i<n;i++){
    if(comp(key, arr+i*size) == 0){
      return arr+i*size;
    }
  }
  return NULL;
}

// if both fields are equal, the structures are equal
// otherwise compare by the sum of two fields
int comp(const void *a, const void *b){
  struct S *aa = (struct S*)a;
  struct S *bb = (struct S*)b;
  if(aa->a == bb->a && aa->b == bb->b){
    return 0;
  }
  if((aa->a + aa->b) - (bb->a + bb->b) > 0){
    return 1;
  }
  return -1;
}

int main(){
  struct S arr[]={{1,2},{3,4},{5,6},{6,7}};
  struct S* value;
  struct S key={5,6};

  value = search(&key, arr, 4, sizeof(struct S), comp);
  if(value){
    printf("%zu\n", value - arr);
  }else{
    printf("nooooo\n");
  }
  return 0;
}

</code>
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