// Example Program 10
// The main objective of this program is to
// give you an idea how to make use of a simple
// relational expression to control the execution
// of a while loop.

// Problem statement:
// Write a program that asks the user to enter the
// present value of a car and displays the number of
// years it takes for the car's trade-in value to be
// $500 or below. Assume that the trade-in value of a
// car is about 70% of its value one year ago.
// Trace the program by hand with present value of
// 1000 dollars.

#include <iostream.h>
int main()
{
   double present_value, trade_in_value;
   int no_of_years = 0;

   // Promt the user
   cout << "Please enter the present value of the car:"<<endl;
   cin >> present_value;

   trade_in_value = present_value;

   while (trade_in_value > 500)
   {
      trade_in_value = 0.7 * trade_in_value;
      ++ no_of_years;
      cout << no_of_years << "   " << trade_in_value << endl;
   }

   cout << "The car will have the trade-in value 500.00 "
	<< " or less in " << no_of_years << " years" << endl;

   return 0;
}


// Example 11.
// The main objective of this example program
// is to demonstrate the use of if statements
// in a program

// Problem statememt: Write a program to determine
// the average score, and the number A's in a class.

// Input: Input is a file ("score.in") containing the
// student ID and the test score for each student in
// the class.

// Output: The program displays on the screen
// the number of students, the average score, and
// the number of A's.


#include <iostream.h>
#include <fstream.h>

int main()
{
    int student_id;
    int test_score;
    int count = 0, a_count = 0;
    double total = 0.0, average_score;

    ifstream infile;

    infile.open("score.in");

    infile >> student_id >> test_score;

    while (infile)
    {
       ++ count;
       total = total + test_score;

       if (test_score >= 90)
	   ++ a_count;

       infile >> student_id >> test_score;
    }

    average_score = total / count;
    cout << "The number of students in the class: "
	 << count << endl;
    cout << "The average score of the class: "
	 << average_score << endl;
    cout << "The number of A's : "<< a_count;

    infile.close();
    return 0;
}




// Example 12.
// The main objective of this example program
// is to demonstrate the use of if-else statements
// in a program

// Problem statememt: Write a program to determine
// the letter grade of a student in a class and also
// the number A's, B's, C's, D's, and F's.

// Input: Input is a file ("score.in") containing the
// student ID and the test score for each student in
// the class.

// Output: The program creates an output file ("grade.out")
// with student ID's and letter grades and also the program
// saves the number of A's, B's, C's, D's, and F's in the
// same output file.


#include <iostream.h>
#include <fstream.h>

int main()
{
    int student_id;
    int test_score;
    int a_count = 0, b_count = 0, c_count = 0;
    int d_count = 0, f_count = 0;

    ifstream infile;
    ofstream outfile;

    infile.open("score.in");
    outfile.open("grade.out");

    outfile << "Student ID    Grade"<<endl;
    outfile << "-------------------"<<endl;

    infile >> student_id >> test_score;

    while (infile)
    {
       outfile << "  "<< student_id<<"    ";

       if (test_score >= 90)
	{
	  ++ a_count;
	  outfile << 'A' << endl;
	}
       else if(test_score >= 80)
	{
	  ++ b_count;
	  outfile << 'B' << endl;
	}
       else if(test_score >= 70)
	{ ++ c_count;
	  outfile << 'C' << endl;
	}
       else if(test_score >= 60)
	 {
	  ++ d_count;
	  outfile << 'D' << endl;
	 }
       else
	 {
	  ++ f_count;
	  outfile << 'F' << endl;
	 }
       infile >> student_id >> test_score;
    }

    outfile << "-------------------"<<endl;

    outfile << "The number of A's : "<< a_count<<endl;
    outfile << "The number of B's : "<< b_count<<endl;
    outfile << "The number of C's : "<< c_count<<endl;
    outfile << "The number of D's : "<< d_count<<endl;
    outfile << "The number of F's : "<< f_count<<endl;

    infile.close();
    outfile.close();

    return 0;
}




// Example Program 13
// This program demonstrates the use of the switch statement
// Problem: For any given date, this program determines
// 	    the day of the week using some formula.
//	    The formula requires that the month of
//	    January and the month of February are
//	    to be considered as 13th and 14th month
//	    of the previous year and also the year
//	    must be greater than or equal to 1752.
//	    You can use this program to find the day of any
//	    event if you know the date.
//	    Try your birtdate to find the day you were
//          born.
// Input:   Input is a file "inday.dat" containing
//          month (mm), day(dd), and year(yyyy). For
//	    example, if the date is 06/12/95, the file
//	    should contain the data set in the form:
//		6   12   1995
// Output:  Output is s file "outday.dat".

#include <fstream.h>
#include <iomanip.h>
int main()
{
   int month, day, year, calc_day, weekday;
   ifstream infile;
   ofstream outfile;

   infile.open("inday.dat");
   outfile.open("outday.dat");
   outfile << "This program determines the day of the"
	   << " week for any given date"<<endl<<endl;

   infile >> month >> day >> year;
   while (infile)
   {
      // Change month for January or February
      // and change year to previous year
      if (month < 3)
      {
	month = month + 12;
	-- year;
      }
      calc_day = day + 2*month + (3*(month+1)/5) + year
		 + year/4 - year/100 + year/400 + 1;
      weekday = calc_day % 7;

      // Undo the changes for month and year
      // for January and Februay
      if (month > 12)
      {
	month = month - 12;
	++ year;
      }


      outfile <<"The date "
	      << setw(2)<<month<<'/'
	      << setw(2)<<day<<'/'
	      << setw(4)<<year
	      << " falls/fell upon a ";
      // Here is the switch statement
      switch(weekday)
      {
	case 0: outfile << "Sunday"<<endl;
		break;
	case 1: outfile << "Monday"<<endl;
		break;
	case 2: outfile << "Tuesday"<<endl;
		break;
	case 3: outfile << "Wednesday"<<endl;
		break;
	case 4: outfile << "Thursday"<<endl;
		break;
	case 5: outfile << "Friday"<<endl;
		break;
	case 6: outfile << "Saturday"<<endl;
      }
      infile >> month >> day >> year;
   }

   infile.close();
   outfile.close();

   return 0;
}