CPT lab05-02 อันที่ถูกน่ะจ๊ะ

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
struct employee {
  char name[128];
  float salary;
};
typedef struct employee Employee;
float total_salary(Employee a[], int len);
int main() {
    int num,i=0,j=0;
    Employee *all,*a;
    FILE *fp;
    printf("Enter num: ");
    scanf("%d",&num);
    all=(Employee *)malloc(num*sizeof(Employee));
    a=(Employee *)malloc(num*sizeof(Employee));
    printf("Input\n");

    fp=fopen("employee.bin","ab+");
    for(i=0; i<num; i++){
        fflush(stdin);
        printf("name: ");
        gets((all+i)->name);
        printf("salary: ");
        scanf("%f",&(all+i)->salary);
        fwrite(&all,sizeof(Employee),1,fp);
    }
    fclose(fp);

    fp=fopen("employee.bin","rb");
    printf("\nOpen File employee.bin \n");
    fread(&a,sizeof(Employee),1,fp);
    printf("Enter num: ");
    scanf("%d",&num);
    for(i=0; i<num; i++){
        printf("Name = %s\n",(a+i)->name);
        printf("Salary = %.2f\n",(a+i)->salary);
    }
    fclose(fp);

    printf("\nTotal Salary = %.1f\n", total_salary(a, num));
    free(a);
    free(all);

    fclose(fp);
    return 0;
}
float total_salary(Employee a[], int len){
    int i;
    float sum=0;
    for(i=0; i<len; i++)
    sum=sum+(a+i)->salary;
    return sum;
}