Understand How a Structure Variable is Returned from a Function

/*
Write a program to understand how a structure variable is returned from a function 
*/

#include<stdio.h>
struct student {
        char name[20];
        int rollno;
        int marks;
           };
void display(struct student);
struct student change(struct student stu);
main( )
{
    struct student stu1 = {"John", 12 , 87 };
    struct student stu2 = {"Mary", 18, 90};
    stu1 = change(stu1);
    stu2 = change(stu2);
    display(stu1);
    display(stu2);
}
struct student change(struct student stu)
{
    stu.marks = stu.marks + 5;
    stu.rollno = stu.rollno - 10;
    return stu;
}

void display(struct student stu)
{
    printf("Name   - %s\t", stu.name);
    printf("Rollno - %d\t", stu.rollno);
    printf("Marks  - %d\n", stu.marks);
}