Sắp xếp điểm học sinh

#include <stdio.h>
typedef struct
{
    char ten[20];
    float diem;
} HS;

int main()
{
    HS a[10],b;
    int n,i,j;
    printf("\nNhap so hoc sinh:");scanf("%d",&n);
    for(i=1;i<=n;i++){
        printf("\nHoc sinh thu %d",i);
        printf("\nTen hoc sinh:");scanf("%s",&a[i].ten);
        printf("Diem :");scanf("%f",&a[i].diem);
    }
    for(i=1;i<=n;i++){
        for(j=i+1;j<=n;j++){
            if(a[i].diem<a[j].diem){
                b=a[i];
                a[i]=a[j];
                a[j]=b;
            }
        }
    }
    printf("\nStt\tten hs\tdiem");
    for(i=1;i<=n;i++){
        printf("\n%3d\t%6s\t%4.1f",i,a[i].ten,a[i].diem);
    }
    return 0;
}