// Example 20
// Problem:
// Write a function that returns the median of three
// numbers. Invoke the function from main().
#include <iostream.h>
int main()
{
   double median(double, double, double);
   double x, y, z;
   cout << "Enter any three numbers"<<endl;
   cin >> x >> y >> z;

   // The following line invokes the function
   cout <<"The median is "<< median(x,y,z)<<endl;
   return 0;
}

double median(double x, double y, double z)
{
  double med_num;
  if (x<=y && y<=z || z<=y && y<=x)
	 med_num = y;
  if (y<=x && x<=z || z<=x && x<=y)
	 med_num = x;
  if (y<=z && z<=x || x<=z && z<=y)
	    med_num = z;
  return med_num;
}



// Example program 21
// Problem:
// Write a function p(x,n) which calculates
// and returns the power of x raised to n.
// Use the function to evaluate a polynomial.

#include <iostream.h>
int main()
{
  double p(double, int);
  double z;
  double poly;

  z = 2.5;
  poly = 2.3*p(z,5)+1.7*p(z,4)-2.0*p(z,3)
	 +1.5*p(z,2)+2.0+0.5*p(z,-1)+2.33*p(z,-2);
  cout << poly <<endl;
  return 0;
}

double p(double x, int n)
{
  int i;
  double product;
  if (n >= 0)
  {
     product = 1;
     for (i=0; i < n; ++i)
	product = product * x;
  }
  else
  {
     product = 1;
     for (i=0; i > n; --i)
	product = product * x;
     product = 1.0 / product;
  }
  return product;
}



// Example program 22
// This program demonstrates the use of reference
// parameters for function calls.
// Problem:
// Write a function that swaps the values of two
// integer variables.
#include <iostream.h>
int main()
{
  void swap(int&, int&);
  int x, y;
  x = 9;
  y = 20;
  cout << x <<"  " << y << endl;
  swap(x,y);
  cout << x <<"  "<< y << endl;
  // Try to invoke the function as swap(56, 8);
  // This will generate error message. why?
  return 0;
}

void swap(int& a, int& b)
{
  int temp;
  temp = a;  // save a in temp
  a = b;     // copy b to a
  b = temp;  // copy temp (prev. a) to b
}




// Example program 23
// This program demonstrates the use of input
// file stream parameters for function calls.
// Problem:
// Write a function that returns the number of words
// in a file.
#include <fstream.h>
int main()
{
  int number_of_words(ifstream&);
  ifstream infile;
  infile.open("ex25.in");
  cout <<"Number of words: "<<number_of_words(infile);
  infile.close();
  return 0;
}

int number_of_words(ifstream& file)
{
  char char1;
  int number = 0;

  file >> char1;
  while(file)
  {
    ++ number;
    // ignore all non whitespace characters
    file.get(char1);
    while (file)
    {
      if(char1 ==' '||char1=='\n'||char1=='\t') break;
      file.get(char1);
    }
    file >> char1;
  }
  return number;
}



// Example program 24
// This program demonstrates how to invoke
// functions with reference parameters, value
// parameters, and input and output file
// stream parameters.

// Problem statement: Calculate the area
// of a triangle from its height and base.
// The program reads unknown number of sets of
// data for height and base from an input file
// and outputs height, base, and area in an
// output file after calculation. If height or
// base is negative then it outputs an error
// message "*** Invalid data ***".

#include <fstream.h>
typedef int Bool;	  // Declare type Bool as int
Bool const TRUE = 1, FALSE = 0;
int main()
{
  void write_heading(ofstream&);  // Prototypes
  void write_line(ofstream&,double,double,double,Bool);
  Bool get_data(ifstream&,double&,double&,Bool&);
  double calculate_area(double,double);

  double height, base, area;
  Bool eof, valid;

  ifstream infile;
  ofstream outfile;
  infile.open("data20.in");
  outfile.open("data20.out");

  write_heading(outfile);
  valid = get_data(infile,height, base, eof);
  while (!eof)
  {
    if (valid)
      {
	area = calculate_area(height, base);
	write_line(outfile,height,base,area,valid);
      }
    else
      write_line(outfile,height,base,area,valid);
  valid = get_data(infile,height, base, eof);
  }

  infile.close();
  outfile.close();
  return 0;
}

void write_heading(ofstream& out1)
{
  out1<<"Height  Base        Area"<<endl;
  out1<<"-----------------------------------";
  out1<<endl;
}

void write_line(ofstream& out2,
		double h, double b, double a, Bool v)
{
  if (v)
    out2 <<h<<"         "<<b<<"         "<<a<<endl;
  else
    out2 <<h<<"         "<<b<<" *** Invalid data ***"<<endl;
}

Bool get_data(ifstream& in,
	      double& h, double& b, Bool& e)
{
 in >> h >> b;
 if(in)
 {
   e = FALSE;
   if ( h < 0 || b < 0) return FALSE;
   return TRUE;
 }
 else
 {
   e = TRUE;
   return FALSE;
 }
}

double calculate_area(double h,double b)
{
 return (h * b /2.0);
}



// Example program 25
// This program demonstrates the use of
// input and output stream variables as reference
// parameters for function calls.
// Problem:
// Write a function that reads an integer amount
// from a file and writes the amount in words in
// a separate file.

#include <fstream.h>
int main()
{
   ifstream infile;
   ofstream outfile;
   void write_in_words(ofstream&,double);
   double number;

   infile.open("ex26.in");
   outfile.open("ex26.out");
   infile >> number;
   while (infile)
   {
     if (number > 0 && number < 1.0e9)
       write_in_words(outfile, number);
     infile >> number;
   }

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

   return 0;
}

void write_in_words(ofstream& out1, double num)
{
  void write_hundreds(ofstream&, int);

  int num_mill, num_thous;

  // Decompose the number millions,
  // thousands etc.
  out1 << num << endl;

  num_mill = num / 1.0e6; // calc. no. of millions
  num = num - num_mill*1.0e6;      // get remainder
  num_thous = num / 1000; // calc. no. of thousands
  num = num - num_thous*1000;      // get remainder


  if (num_mill > 0)
  {
     write_hundreds(out1, num_mill);
     out1 <<" million ";
  }
  if (num_thous > 0)
  {
     write_hundreds(out1, num_thous);
     out1 <<" thousand ";
  }
  write_hundreds(out1, (int)num);
  out1 << endl;
  return;
}

void write_hundreds(ofstream& out2, int num2)
{
  void write_1_to_19(ofstream&, int);
  void write_20_to_90(ofstream&, int);
  int num_hundred, num_tenth;
  num_hundred = num2/100;
  num2 = num2%100;
  num_tenth = 0;
  if (num2 >=20)
  {
    num_tenth = num2/10;
    num2 = num2%10;
  }

  if (num_hundred > 0)
  {
    write_1_to_19(out2,num_hundred);
    out2 <<" hundred ";
  }
  if (num_tenth > 0)
  {
     write_20_to_90(out2,num_tenth);
     out2 <<" ";
  }
  if (num2 > 0)
  {
     write_1_to_19(out2,num2);
  }
}

void write_1_to_19(ofstream& out3, int num3)
{
  switch(num3)
  {
    case 1: out3 << "one"; break;
    case 2: out3 << "two"; break;
    case 3: out3 << "three"; break;
    case 4: out3 << "four"; break;
    case 5: out3 << "five"; break;
    case 6: out3 << "six"; break;
    case 7: out3 << "seven"; break;
    case 8: out3 << "eight"; break;
    case 9: out3 << "nine"; break;
    case 10: out3 <<"ten"; break;
    case 11: out3 <<"eleven";break;
    case 12: out3 <<"twelve";break;
    case 13: out3 <<"thirteen";break;
    case 14: out3 <<"fourteen";break;
    case 15: out3 <<"fifteen";break;
    case 16: out3 <<"sixteen";break;
    case 17: out3<<"seventeen";break;
    case 18: out3<<"eighteen";break;
    case 19: out3<<"ninteen";break;
  }
}
  void write_20_to_90(ofstream& out3,int num3)
  {
    switch (num3)
    {
      case 2: out3 <<"twenty"; break;
      case 3: out3 <<"thirty"; break;
      case 4: out3 <<"fourty"; break;
      case 5: out3 <<"fifty"; break;
      case 6: out3 <<"sixty"; break;
      case 7: out3 <<"seventy"; break;
      case 8: out3 <<"eighty"; break;
      case 9: out3 <<"ninety"; break;
    }
  }