// ENGR 131 Monday 3:30 Recitation (Amanda Rohn)
// HW 4 - The Obsessive Student's Calculator
// Solution

#include <iostream>
#include <cctype>
#include <cassert>
#include <iomanip>

using std::cout;
using std::cin;
using std::endl;
using std::setprecision;
using std::fixed;
using std::showpoint;

int GetInteger(const char* prompt, int min, int max);
double GetDouble(const char* prompt, double min, double max);
char GetChar(const char* prompt);
int QPoints(char grade);

int main()
{
	cout << "Welcome to the Obsessive Student's Calculator" << endl;

	int choice;
	double gpa;
	double top_terms, bottom_terms;
	int cred_hrs;
	char lgrade;	//letter grade
	int pts;		//points for letter grade: A=4, B=3, etc.
	int desired_percent;
	int points_needed, total_points, current_points;
	int system;		//1 for point, 2 for percent
	int percent_needed, current_percent, exam_percent;
	double gpa_earned, gpa_needed;
	int current_credits, earned_credits;

	for(;;)
	{
		bottom_terms = top_terms = 0;
		
		cout << "\nWhat do you need to know?\n"
			 << "1. What's my GPA?\n"
			 << "2. How well do I have to do on the final to get my grade?\n"
			 << "3. How well do I have to do this semester to keep my scholarship?\n"
			 << "4. I already know too much. Let me out of here.\n";

		choice = GetInteger("Enter your choice", 1, 4);

		switch(choice)
		{
		case 1: cout << "\nFor each class, enter your letter grade and the credit hours.\n"
					 << "(Enter 'Q' as a letter grade to quit entering)\n";
			    for(;;)
				{
					for(;;)		//get letter grade from user
					{
						lgrade = toupper(GetChar("\nLetter Grade"));
						if(lgrade != 'A' && lgrade != 'B' && lgrade != 'C' && lgrade != 'D' && lgrade != 'F' && lgrade != 'Q')
							cout << "\nLetter grades are A, B, C, D, or F (Q to quit). Try again.";
						else break;
					}
					if(lgrade == 'Q') break;

					pts = QPoints(lgrade);

					cred_hrs = GetInteger("Credit hours", 0, 4);	//get credit hours from user

					top_terms += (cred_hrs * pts);
					bottom_terms += cred_hrs;
				}

				if(lgrade == 'Q' && bottom_terms == 0) break;

				gpa = top_terms / bottom_terms;

				cout << "\nYour GPA is " << fixed << showpoint << setprecision(3) << gpa << endl;
				break;

		case 2: system = GetInteger("\nIs your class's grading based on the point system (1) or percentage system (2)?", 1, 2);
				if(system == 1)	//point system
				{
					total_points = GetInteger("\nHow many points are possible in the course?", 0, 10000);
					current_points = GetInteger("How many points do you have now?", 0, total_points);
					desired_percent = GetInteger("What percentage grade do you want to end up with?", 0, 100);
					
					points_needed = desired_percent * .01 * total_points - current_points;

					cout << "\nYou need " << points_needed << " points on the exam to get a " << desired_percent << "% in the course." << endl << endl;
				}
				else if(system == 2) //percentage system
				{
					current_percent = GetInteger("\nWhat is your current percentage grade?", 0, 100);
					exam_percent = GetInteger("What percentage of the total grade is the exam worth?", 0, 100);
					desired_percent = GetInteger("What percentage grade do you want to end up with?", 0, 100);
					
					percent_needed = (desired_percent - current_percent * (1 - exam_percent * .01)) / (exam_percent * .01);
				
					cout << "\nYou need a " << percent_needed << "% on the exam to get a " << desired_percent << "% in the course." << endl;
				}

				break;

		case 3:	earned_credits = GetInteger("\nHow many credits have you earned so far, not including this semester?", 0, 1000);
				gpa_earned = GetDouble("What is your current GPA, not including this semester?", 0, 4.000);
				current_credits = GetInteger("How many credit hours are you taking this semester?", 0, 30);

				gpa_needed = ( 3 * (current_credits + earned_credits) - gpa_earned * earned_credits) / current_credits;
		
				cout << "\nYou need to get a " << fixed << showpoint << setprecision(3) << gpa_needed << " this semester to keep your scholarship.\n";

				break;

		}

	if(choice == 4)
		break;
	}

	cout << "\nHappy studying!\n\n";

	return 0;
}

/****FUNCTION DEFINITIONS****/

int GetInteger(const char* prompt, int min, int max)
{
    assert(min < max);

    int number;
    for(;;)
    {
        cout << prompt << ": ";
        cin >> number;

        if (cin.fail())
        {
            cout << "Please enter an integer." << endl;
            cin.clear();
            cin.ignore(1024,'\n');
        }
		else if (cin.peek() != '\n')
        {
            cout << "Please enter only an integer." << endl;
            cin.ignore(1024,'\n');
        }
		else if (number < min || number > max)
        {
            cout << "Please enter a number between " <<
                min << " and " << max << "." << endl;
            cin.ignore(1024,'\n');
        }
		else
        {
            cin.ignore(1024,'\n');
            return number;
        }
    }
}


double GetDouble(const char* prompt, double min, double max)
{
    assert(min < max);

	double number;
    for(;;)
    {
        cout << prompt << ": ";
        cin >> number;

        if (cin.fail())
        {
            cout << "Please enter a number." << endl;
            cin.clear();
            cin.ignore(1024,'\n');
        }

        else if (cin.peek() != '\n')
        {
            cout << "Please enter only a number." << endl;
            cin.ignore(1024,'\n');
        }

        else if (number < min || number > max)
        {
            cout << "Please enter a number between " <<
                min << " and " << max << "." << endl;
            cin.ignore(1024,'\n');
        }

        else
        {
            cin.ignore(1024,'\n');
            return number;
        }
    }
}

char GetChar(const char* prompt)
{
    char input;

    for(;;)
    {
        cout << prompt << ": ";
        cin >> input;

        if (cin.fail())
        {
            cout << "Please enter a character." << endl;
            cin.clear();
            cin.ignore(1024,'\n');
        }
		else if (cin.peek() != '\n')
        {
            cout << "Please enter only one character." << endl;
            cin.ignore(1024,'\n');
        }
		else
        {
            cin.ignore(1024,'\n');
            return input;
        }
    }
}

int QPoints(char grade)
{
	grade = toupper(grade);

	assert(grade == 'A' || grade == 'B' || grade == 'C' || grade == 'D' || grade == 'F');

	int pts;

	switch(grade)	//assign appropriate # of points according to letter grade
	{
		case 'A':	pts = 4;
					break;
		case 'B':	pts = 3;
					break;
		case 'C':	pts = 2;
					break;
		case 'D':	pts = 1;
					break;
		default:	pts = 0;
	}

	return pts;
}