感觉是结构体内的函数有问题，但是不知道怎么改

#include<stdio.h>
#include<math.h>
#define N 1000
struct student
{
    long id;//学号
    int study;//学业成绩
    int suzhi;//素质拓展
    double all;//综合成绩
    int sum() {return study+suzhi;}//总分 
};
typedef struct student students;

void decide(students *a,int n){
    for(int i=0;i<n;i++){
        if(a[i].all>=80 && a[i].sum>140){
            printf("Excellent\n");
        }else{
            printf("Not excellent\n");
        }
    }
}
//
int main()
{
    students a[N];
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%ld %d %d",&a[i].id,&a[i].study,&a[i].suzhi);
        a[i].all=a[i].study*0.7+0.3*a[i].suzhi;
    }
    decide(a,n);
    return 0;
}