Passing array of structure to fread and fwrite function in C - c

Question

I have a questions regarding the fread() and fwrite() function in c.
Talking about the first parameter void* If i am dealing with array of structure and want to pass an entire array what should i use &arrayName or arrayName.
Now I am trying to input some data from users create a student.txt file and store the data in that file and again read that data from the same file and display it.
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main()
{
struct dob
{
int year,month,date;
};
struct student
{
int roll;
char name[20],address[20],faculty[30];
struct dob a;
};
struct student s1[2],s2[2];
FILE *fp;
fp = fopen("student.txt","w+b");
if(fp == NULL)
{
printf("Cannot open file");
exit(0);
}
for(int i = 0 ; i < 2 ; i++)
{
fflush(stdin);
printf("Enter the name of student %d\n",i+1);
scanf("%[^\n]s",s1[i].name);
fflush(stdin);
printf("Enter address\n");
scanf("%[^\n]s",s1[i].address);
fflush(stdin);
printf("Enter roll no\n");
scanf("%d",&s1[i].roll);
fflush(stdin);
printf("Enter faculty\n");
scanf("%[^\n]s",s1[i].faculty);
fflush(stdin);
printf("Enter the Birth year\n");
scanf("%d",&s1[i].a.year);
printf("Enter the Birth month\n");
scanf("%d",&s1[i].a.month);
printf("Enter the Birth date\n");
scanf("%d",&s1[i].a.date);
}
fwrite(&s1,sizeof(s1),2,fp);
rewind(fp);
fread(&s2,sizeof(s2),2,fp);
for(int i = 0 ; i < 2 ; i++)
{
printf("Name : %s\n Address = %s\n Faculty = %s\n Roll = %d\n year = %d\n month = %d\n date =
%d\n",
s2[i].name,s2[i].address,s2[i].faculty,s2[i].roll,s2[i].a.year,s2[i].a.month,s2[i].a.date);
}
fclose(fp);
return 0;
}
I am asking it because both of them works for my above code.But How?
I am talking about this line
fwrite(&s1,sizeof(s1),2,fp);
fread(&s2,sizeof(s2),2,fp);
Here s1 and s2 works without & as well