Throw away members in qsort

Code:

---

/* I need help
How can I move away from qsort all members that are not have enought points */
/* I wanna do some filer function (base on qsort) that throw away all field elements that doesent satisfy criterion (what is incoming argument of function filer)*/
/* In function does_have_enought_points all members with let's say udenr 100 points. drop out*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX 1024
#define MAXS 128

struct student{
      char name[MAX];
      char lastname[MAX];
      int points;
};

typedef struct student STUDENT;

int does_have_enought_points( const void *a )
{
}

void filter( void *base, int *num, int width, int(*fn_criterion)(const void*))
{
}


int compare_points(const void *a, const void *b)
{
    return ( ((STUDENT*)a)->points - ((STUDENT*)b)->points);
}


void load( STUDENT a[MAXS], int n)
{
    int i;
    for(i = 0; i < n; i++)
    {
          printf("Insert name: "); scanf("%s", &a[i].name);
          printf("Insert lastname: "); scanf("%s", &a[i].lastname);
          printf("Insert points: "); scanf("%d", &a[i].points);
    }
}

void write_out( STUDENT a[MAXS], int n)
{
    int i;
    for( i = 0; i < n; i++ )
    {
          printf("%s ", a[i].name);
          printf("%s ", a[i].lastname);
          printf("%d ", a[i].points);
          printf("\n");
    }
}

int main()
{
    STUDENT a[MAXS];
    int n = 0;

    printf("How many students do you wanna enter?\n");
    scanf("%d", &n );
    load( a, n );

    filter( a, &n, sizeof(STUDENT), does_have_enought_points);
    write_out( a, n );

    qsort( a, n, sizeof(STUDENT), compare_points);
    write_out( a, n );

    return 0;
}

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You sort the array in decreasing score.
Search from the start of the array for the minimum score you'll accept.
Throw the remainder of the array away.

Can you please explain me what am I calling here. I forgot to mention that I dont understand it all.
I got this for homework.

Code:

---

int does_have_enought_points( const void *a )
{
...
}

void filter( void *base, int *num, int width, int(*fn_criterion)(const void*))
{
...
}

---

I fail to see what those functions have to do with qsort.
Sure, it's qsort-like, seeing as you're passing pointers to functions.

Can you show how you're trying to use those functions.

Rough Idea

Code:

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int does_have_enought_points( const void *a )
{
  const struct student *p = a;
  return p->points >= 100;
}

void filter( void *base, int *num, int width, int(*fn_criterion)(const void*))
{
  char *p = base;  // so ptr math works
  char *q = base;
  int i, j = 0;
  for ( i = 0 ; i < *n ; i++ ) {
    if ( fn_criterion( p ) ) {
      // copy a passing record to the next passing slot
      memmove( q, p, width );
      q += width;
      j++;
    }
    p += width;
  }
  *n = j; // number of passing answers
}

---

Thank you.
What I have done is copy paste your code and it worked only one thing is that i rename two times *n in *num. And it worked.

Now I see that qsort function under is completly unneed.
What I have done is that I insert few people and all people who has under some sum of points. Are of. They are not on the list.

Thank you Salem!