// Example Program 14 : While loop
// Write a program that finds the largest
// in a series of positive numbers entered
// by the user.
// When the user enters 0 or a negative number,
// the program displays the largest number and
// stops.
// Walk through the program for some numbers.
// Also, think about how to modify the program
// to find the smallest.

# include <iostream.h>
int main()
{
   int largest, number;
   cout <<"Enter a number : ";
   cin >> number;
   cout << endl;
   largest = number;

   // Continue processing until number is
   // zero or negative
   while (number > 0)
   {
     if (largest < number)   // Check and
	 largest = number;   // update
     cout <<"Enter a number : ";
     cin >> number;
     cout << endl;
   }

   cout <<"The largest number is "<<largest<<endl;

   return 0;
}


// Example Program 15: While loop
// Write a program that asks for a positive
// number and then displays the number
// with its digits reversed. That is, 523 will
// be displayed as 325.

#include <iostream.h>
int main()
{
   long number;
   cout << "Enter a positive number : ";
   cin >> number;
   cout << endl;

   cout << "The number with its digits reversed is ";
   while (number)
   {
     cout << (number % 10);
     number = number / 10;
   }
   return 0;
}


// Example 16: while loop
// Write a program that asks the user to enter
// two integers, then calculates and displays their
// greatest common divisor.
#include <iostream.h>
int main()
{
  int m, n, remainder;
  cout <<"Enter the first integer : ";
  cin >> m;
  cout <<"Enter the second integer : ";
  cin >> n;

  remainder = m % n;
  m = n;
  n = remainder;
  while (n)
  {
    remainder = m % n;
    m = n;
    n = remainder;
  }
  cout <<"Greatest common divisor: "<<m<<endl;

  return 0;
  }

// Example 17: while loop
// Converting all lower case characters
// to upper case characters.
// Input File:	data.in
// Output File:	data.out
// Try modifying the program to convert
// uppercase to lowercase characters
#include <fstream.h>
int main()
{
  ifstream infile;
  ofstream outfile;
  char ch;

  infile.open("data.in");
  if(!infile) {cout<<"Error";return 0;}
  outfile.open("data.out");
  if(!outfile) {cout<<"Error";return 0;}
  
  // Read a charater
  infile.get(ch);
  while (!infile.eof())
  {
    // check if it is a lower case
    // character
    if(ch >= 'a' && ch <= 'z')
       ch = ch - 'a' + 'A';

    // write the character
    outfile << ch;
    // get the next character
    infile.get(ch);
  }

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

  return 0;
}




// Example 18: Nested while loop
// Write a program to display a tax table in the
// following form.
// Amount		Tax Rate
// ------------------------------------------------------
//           4.0   4.5%  5.0%   5.5%   6.0%   6.5%   7.0%
// 100.00
// 200.00
// 300.00
//   .
//   .
//   .
// 1000.00
// -----------------------------------------------------
#include <iostream.h>
#include <iomanip.h>
int main()
{
  double tax_rate;
  double amount;


  cout.setf( ios::fixed, ios::floatfield );
  cout.setf( ios::showpoint );


  cout <<"   Amount                 Tax Rate"<<endl;
  cout <<"----------------------------------"
       <<"-------------------------------"<<endl;

  cout <<"        ";

  cout << setprecision(1);
  tax_rate = 0.04;
  while (tax_rate < 0.075)
  {
    cout <<setw(7)<<(tax_rate*100)<<'%';
    tax_rate = tax_rate + 0.005;
  }
  cout << endl;
  cout<<setprecision(2);
  amount = 100.00;
  while (amount < 1050.00)
  {
    cout << setw(8)<<amount;
    tax_rate = 0.04;
    while (tax_rate < 0.075)
    {
      cout <<setw(8)<<(tax_rate*amount);
      tax_rate = tax_rate + 0.005;
    }
    cout << endl;
    amount = amount + 100.00;
  }
  cout <<"----------------------------------"
       <<"-------------------------------"<<endl;
  return 0;
}




// Example 19: Nested while loop
// This program determines whether a given number
// is a perfect number. Recall the algorithm
// about perfect numbers discussed in the class
// from course notes at the beginning of the
// semester.
#include <iostream.h>
#include <math.h>
int main()
{
  int perfect_number, divisor_number;
  int divisor_sum, remainder;
  int divisor, end_of_data , last_divisor , perfect;
  const int no_more_data = 0 , initial_sum = 1;
  const int first_divisor = 2;

  cout <<"Enter a possible perfect number or 0 to quit"<<endl;
  cin >> perfect_number;
  end_of_data = ( perfect_number <= no_more_data);

  while (!end_of_data)
  {
    divisor_number = first_divisor;
    divisor_sum = initial_sum;
    last_divisor = (divisor_number > sqrt(perfect_number));

    while (!last_divisor)
    {
      remainder = perfect_number % divisor_number;

      divisor = (remainder == 0);
      if (divisor)
	divisor_sum= divisor_sum + divisor_number
	   + perfect_number/divisor_number;
      divisor_number = divisor_number + 1;
      last_divisor = (divisor_number > sqrt(perfect_number));
    }
    perfect = (divisor_sum == perfect_number);
    if(perfect)
      cout <<"The number "<<perfect_number<<" is PERFECT"<<endl;
    else
      cout <<"The number "<<perfect_number<<" is NOT perfect"<<endl;
    cout <<"Enter a possible perfect number or 0 to quit"<<endl;
    cin >> perfect_number;
    end_of_data = (perfect_number <= no_more_data);
  }
  return 0;
}