/* This program demonstrates
 * 1. An introduction to structures
 * 2. Nested Structs
 * 3. Dynamic Struct variables
 * 4. Arrays of 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()
{
    //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);

    /* We can use the new keyword to create a dynamic struct variable */
    Student *st1 = new Student;

    // We can use the same functions, but we would need to dereference to match
    // the function signature.
    readStudent(*st1);
    cout<<"Student Details:\n";
    printStudent(*st1);

    /* The Arrow Operator: We use the dot operator to access the data element of an struct
     * variable.
     * If we have a pointer to a struct variable instead, we need to use the arrow operator (->),
     * as shown below:
     */
    cout<<st1->name <<" is "<< 2021 - st1->dateOfBirth.year << " years old"<<endl;
    delete st1;

    /* We can create an ins-stack array of struct variables.
     * It is still an array. It is contiguous in memory, 0-indexed, etc.
     */
    Student arr[10];
    int n;
    cout<<"Enter the number of students: ";
    cin>>n;
    for(int i=0; i<n; i++)
    {
        cin.ignore();       // We need this to premove the preceding newline
        readStudent(arr[i]);

    }

    /* Calculating class average
     * We iterate through the array, adding up all the grades of all the students.
     * We then divide by the number of students, and then 3, to get the course average.
     */
    double sum = 0;
    for(int i=0; i<n; i++)
    {
        for(int j=0; j<3; j++)
        {
            /* arr[i] will take us to the student variable element of the array
             * arr[i].grades takes us to the grades array data element of the student
             * arr[i].grades[j] takes us to each individual grade of the student
             */
            sum = sum + arr[i].grades[j];
        }

    }
    double avg = sum / n / 3;
    cout<<"Class average: "<<avg;

    /* Print each individual student using the function
     */
    for(int i=0; i<n; i++)
    {
        cout<<"Student "<< i+1<<":\n";
        printStudent(arr[i]);
        cout << endl;
    }
    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;
}