/* This program demonstrates in-stack arrays of structs */

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

// We use the same structs from last class
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
// We use the same functions from last class

void printDate(Date d);

Date readDate();

void printStudent(Student s);

void readStudent( Student &s);

// function to calculate the class average
double classAverage(Student arr[], int size);

int main()
{
    /* We can create an array of structs. */
	Student arr[10];
    int num;
    cout<<"Enter the number of students: ";
    cin>>num;

	cout<<"enter student data: ";
	
    for(int i=0; i< num; i++)
    {
        cin.ignore();       // Remove the preceding newline
        readStudent(arr[i]);       // use same as previous array
    }

	cout<<"Printing student details: "<<endl;
	for(int i=0; i<num; i++)
	{
		printStudent(arr[i]);
	}
   
    cout<<"Class average: "<<classAverage(arr, num)<endl;

    /* Accessing members of internal struct variable
	 * Here, we calculate the age of students by subtracting the year they were born
	 * from the current year
     */
    
    for(int i=0; i<num; i++)
    {
        cout<<arr[i].name << " is "<< 2022 - arr[i].dateOfBirth.year<<" years old"<<endl;
    }
	
	/* We can create a single dynamic struct variable through a pointer and the
     * new operator.
     * Once we have a dynamic variable, individual elements of the struct are accessed
     * through the arrow operator ->, not the dot operator
     */

    Student *s = new Student;

    // We need to dereference to pass by reference
    cout<<"enter the student data: ";
	readStudent(*s);
	
	printStudent(*s);
	
	cout<<s->name <<" is "<< 2022 - s->dateOfBirth.year<<" years old"<<endl;
	
	// delete when we no longer need it
	delete s;
    
    return 0;
}

/* This function accepts an array of Student structs as the parameter and
 * calculates the class average by adding the grades of each individual student
 */
double classAverage(Student arr[], int size)
{
	 double sum =0;

    /* Calculating class average for this array */
    for(int i=0; i<size; 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 / size / 3;
	return avg;
}

/* 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];
    cin.ignore();   // remove newline after entering grades
    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;
}