/*
 **************************************************************************
 * Program name : 005_Area_of_triangle (Version 1.00)                     *
 * Author       : Duck Wong                                               *
 * Language     : C / C++                                                 *
 * Compiler     : Boodshed Dec-C++ compiler Ver 3.95                      *
 * Computer     : PII350                                                  *
 * O/S          : Windows 98                                              *
 **************************************************************************
 * Version 1.00 : 2000/06/04 - first version                              *
 **************************************************************************
 * Description  : (a) intut the length of 3 sides of a triangle           *
 *                (b) calculate the area of the triangle                  *
 *                (c) output results                                      *
 **************************************************************************
*/
#include <iostream>
#include <stdlib.h>
#include <iomanip.h>                                                 // Note (1)

int main()
{
 // part 1 : declaration
 float side_A, side_B, side_C, area;
 char YN;

 do                                                                  // Note (2)
   {
    // part 2 : input
    cout << "   Calculate the area of a triangle (Version 1.0)\n\n";
    cout << "\a\t" << "Enter the length of Side A : ";
    cin  >> side_A;
    cout << "\a\t" << "Enter the length of Side B : ";
    cin  >> side_B;
    cout << "\a\t" << "Enter the length of Side C : ";
    cin  >> side_C;
    cout << "\n";

    // part 3 : calculate & output the result
    if (side_A+side_B<side_C || side_B+side_C<side_A ||side_C+side_A<side_B)
      cout << "   Involid length of side(s)!\a\n\n";
    else
      {
       area =  sqrt(((side_A+side_B+side_C)/2)*
                   (((side_A+side_B+side_C)/2)-side_A)*
                   (((side_A+side_B+side_C)/2)-side_B)*
                   (((side_A+side_B+side_C)/2)-side_C));
       cout << "   The ares is : "
            << setprecision(5)        // value prints with 5 decimal digits
            << setiosflags(ios::fixed |ios::showpoint)
            << area << "\n\n" << endl;
      };

    // part 4 : try again
    cout << "\a   Try again (Y/N) : ";
    cin  >> YN;
    cout << "\n\n";
   } while (YN == 'Y' || YN == 'y');                                 // Note (3)

 system("PAUSE");
 return 0;
}

/* Notes
   (1) Use the '#include <iomanip.h>' because this program needs to change
       the format of the floating-point values. The default format is :
       prints w/ 4 decimal digits.

   (2) To execute a while statement, the computer first determine whether the
       expression is true or false. If expression is true, the computer execute
       action and return to the top of the loop. The computer repeat this
       process until the expression is false.

       The do while statement is similar to the while statement; the only
       different is that the expression controlling the loop is tested at the
       bottom of the loop. That means the body of the loop is always executed
       at least once (same as REPEAT...UNTIL statement in PASCAL).

   (3) Logical operators :
         &&=AND , 
         ||=OR  ,
         ! = NOT

       i.e. while (YN == 'Y' || YN == 'y')
       means repeat the loop if YN = 'Y' or 'y'
*/