gradebook

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

#define N_student 4
int i,n;

struct student
{
 char id[10];
 char name[50];
 char dob[10];
 double marks1, marks2, marks3;
 double average_marks;
 char grade;
} students [N_student];

void assigngrade();
void printavg();

main()
{
   char buffer[50];
   double total;
   for (i=0; i<N_student; i++)
   {
    printf("Enter Student ID no: \n");
    scanf("%s", students[i].id);
    printf("Enter Student name: \n");
    scanf("%S", students[i].name);
    printf("Enter Date of Birth (dd/mm/yyyy): \n");
    scanf("%s", students[i].dob);
    printf("Enter marks obtained for test1: \n");
    scanf("%d", &students[i].marks1);
    printf("Enter marks obtained for test2: \n");
    scanf("%d", &students[i].marks2);
    printf("Enter marks obtained for test3: \n");
    scanf("%d", &students[i].marks3);
    total = (double)students[n].marks3 + (double) students[n].marks2 + (double)students[n].marks1;
    students[n].average_marks = (double)(total/3);
    assigngrade();
   }
    printf("You've entered the students details. \n");

    printavg();

    return 0;
}

void assigngrade()
{
    if ((students[n].average_marks<=4) && (students[i].average_marks>3))
        {
        students[i].grade='A';
        }
    else if ((students[i].average_marks<=3) && (students[i].average_marks>2))
        {
        students[i].grade='B';
        }
    else if ((students[i].average_marks<=2) && (students[i].average_marks>1))
        {
        students[i].grade='C';
        }
    else if ((students[i].average_marks<=1)    && (students[i].average_marks>=0))
        {
        students[i].grade='D';
        }
}

void printavg()        /* prints the average grade for a student */
{
for (i=0; i<N_student; i++)
{

    printf ("Student Id=");
    printf ("%s\n",students[i].id);
    printf ("Student Name=");
    printf ("%s\n",students[i].name);
    printf ("Student Average marks=");
    printf ("%.2f\n",students[i].average_marks);
    printf ("Student Grade=");
    printf ("%c\n",students[i].grade);
}

}