ขอบพระคุณพี่ๆทุกคนครับ
#include <stdio.h>
int main (void)
{
    // Local declarations
int size = 5 , i;
    float sum = 0, ave;
    int smallest, temp, current, walk, j=1, last=size - 1;
    int list[size];
    //Statements
printf("Enter score Student\n");
//Create and fill variable-length array
    float aray[size];
    //Fill array and calculate sum
for(i=0; i<size; i++)
        {
        printf("Student %d : ",i+1);
        scanf("%f", &aray[ i ]);
        sum += aray[ i ];
}
ave = sum / size;
    //Print average
    printf("\nAverange is : %.1f", ave);
    printf("\n\nStuden Who Score below average");
    for(i=0;i<size;i++)
    {
   if(aray<ave)
   {
   printf("\nStudent %d : %.1f", i+1, aray);
   }
    }
    printf("\n");
    for(current=0;current<last;current++)
    {
        smallest=current;
        for(walk=current+1;walk<=last;walk++)
   {
       if(aray[walk]>aray[smallest])
            smallest=walk;
            temp=aray[current];
            aray[current]=aray[smallest];
            aray[smallest]=temp;
            j++;
        }
        if(j == size)
   {
     printf("\nRating ranking from descanding order \n");
     for(i=0;i<size;i++)
       {
       printf("Score No.%d : %.1f\n", i+1, aray);
   }
   }
   return 0;
    }
}