/* This program demonstrates
 * 1. An introduction to structures
 * 2. Nested Structs
 *
 * A structure is a way to create a composite data type.
 * So far, we have been working with atomic/primitive data types that can only
 * hold one kind of data. structures allow us to bundle up several data elements
 * into one unit, while still allowing us to access the individual elements.
 * A structure can be used as a regular data type.
 *
 * We can create variables of the structure type, pass it to functions and
 * return it from functions
 * With respect to functions, struct variables pass by value.
 *
 * This program also demonstrates advanced struct concepts
 * 1. Structs can contain arrays as data elements
 * 2. Structs can be nested - ie structs can contain other struct variables
 */

#include<iostream>
#include<cstring>
#include<string>
using namespace std;

/* To create a structure, we use the keyword "struct" followed by the name of the
 * structure (we choose this). We then open a code block and declare all the variables
 * for the elements of the structure.
 * We only declare them. Structure elements should NOT be initialized (given values)
 * in the structure declaration unless they are consts.
 * the structure declaration ends with a semicolon.
 * The following line declares a Date structure with 4 data members
 */
struct Date
{
    int month, day, year;
    char dayOfWeek[15];
};

/* Student structure
 * name - string
 * major - string
 * GPA - float
 * EMPL - long
 * grades - array of 3 floats
 * datOfBirth - Date struct variable
 */
struct Student
{
    string name, major;
    float gpa;
    long empl;
    float grades[3];
    Date dateOfBirth;
};

// If a function uses a structure, it has to be declared after the struct declaration

void printDate(Date d);

Date readDate();

void printStudent(Student s);

void readStudent( Student &s);

int main()
{
    /* To declare a structure variable, just use the Structure name as a data type.
    * Just like an array can be initialized with set notation, we can initialize
    * structures with set notation as well. Any composite types in the structure
    * (like arrays, other structures) need their own set of {}
    */
    Date today = {11, 15, 2021, "Monday"};

    /* To access an internal element of the structure variable, we use the dot (.) operator */
    cout<<"Today is "<< today.dayOfWeek<<", "<< today.month<<"/"<< today.day
          <<"/"<< today.year<<endl;

    /* We can pass structures into a function just like regular variables.
    * individual structure variables always pass by value. */
    printDate(today);

    // copy using assignment
    //copying a structure variable only copies out the data elements' values
    //no other connection between the two variables.
    Date d2 = today;
    cout<<"\nAfter copy: d2:\n";
    printDate(d2);

    d2.day = 17;

    // since the dayOfWeek element is a c-sting, we can call c-string functions with it
    strcpy(d2.dayOfWeek, "Wednesday");
    cout<<"After change: today:\n";
    printDate(today);
    cout<<"\nd2: \n";
    printDate(d2);

    // We can store the value returned from the readDate function in a Date variable
    Date userDate = readDate();
    cout<<"User entered date: ";
    printDate(userDate);
	
	//Initialize the structure variable by individually initializing the data elements
    Student s;
    s.name = "Gary";
    s.empl = 25465;
    s.gpa = 3.8;
    s.major = "meow";

    printStudent(s);    // will print junk for uninitialized parts

    /* We can also initialize using set notaion, but each internal composite
     * data memeber needs its own {} */
    Student t = {"Spongebob", "Boating", 2.67, 389482,
                 {75,78,91}, {7, 14, 1987, "Friday"}};

    printStudent(t);

    //this function uses a Student variable as a reference variable
    Student s1;
    readStudent(s1);
    cout<<"Student Details:\n";
    printStudent(s1);

    return 0;
}
/* This function takes a Date variable as a parameter and the prints the elements */
void printDate(Date d)
{
    cout<<d.dayOfWeek<<", ";
    /* Internal elements of structure variables can be used like regular variables,
    * as values in calculations, in conditional statements, loops,etc.
    * For example, we can use the "m" element of the Date structure variable "birthday"
    * in a switch statement, to get the name of the month.
    */
    switch(d.month)
    {   case 1: cout<<"January";
            break;
        case 2: cout<<"February";
            break;
        case 3: cout<<"March";
            break;
        case 4: cout<<"April";
            break;
        case 5: cout<<"May";
            break;
        case 6: cout<<"June";
            break;
        case 7: cout<<"July";
            break;
        case 8: cout<<"August";
            break;
        case 9: cout<<"September";
            break;
        case 10: cout<<"October";
            break;
        case 11: cout<<"November";
            break;
        case 12: cout<<"December";
            break;
        default: cout<<"Invalid Month";
    }
    cout<<" "<<d.day<<" "<<d.year<<endl;
}

/* This function creates a Date variable, reads in the values and returns it. */
Date readDate()
{
    Date var;
    cout<<"Enter a date: (Day of the week, month/day/year): ";
    cin.getline(var.dayOfWeek, 15, ',');
    char junk;
    cin>>var.month>> junk>> var.day>>junk>>var.year;
    return var;
}

/* This function accepts a structure variable and prints out the details in the structure
* We use the dot (.) operator to access individual elements.
*/
void printStudent( Student s)
{
    cout<<s.name <<" ( EMPLID "<< s.empl<<") is a "<< s.major<<" major with a "
        << s.gpa<<" GPA."<<endl<<"3 grades: ";
    for(int i=0; i<3; i++)
        cout<<s.grades[i]<<"\t";
    cout<<"\nDate if birth: ";
    printDate(s.dateOfBirth);
}
/* This function reads the values into a structure variable.
 * Since structure variables usually pass by value, we use a reference variable
 * to read. That way, any changes we make to the individual elements while
 * reading in values from the user will be retained across the function call.
 */
void readStudent (Student &s)
{
    cout<<"Name: ";
    getline(cin, s.name);
    cout<<"major: ";
    getline(cin, s.major);
    cout<<"GPA: ";
    cin>>s.gpa;
    cout<<"EMPLID: ";
    cin>>s.empl;
    cout<<"3 grades: ";
    for(int i=0; i<3;i++)
        cin>>s.grades[i];
    cout<<"Date of birth (Day of Week, m/d/y): ";
    cin.getline(s.dateOfBirth.dayOfWeek, 15, ',');
    cin>>s.dateOfBirth.month;
    cin.ignore();
    cin>>s.dateOfBirth.day;
    cin.ignore();
    cin>>s.dateOfBirth.year;
}