Computing Concepts with C++ Essentials, 2nd ed.
Laboratory Notebook
Chapter 4 - Decisions

Cay S. Horstmann
Geof Pawlicki

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Lab Objectives

To gain experience in

R1. The if statement

In C++, decisions to do or not to do something can be made by using the statement if (test expression). The test expression must be an expression that can be evaluated as either true or false. If it evaluates to true, a succeeding statement or group of statements enclosed in { . . . }, called a block statement will be executed.

How many circles will be drawn when the following code is executed with radius = 7 ?

#include "ccc_win.cpp"

int main()
{   double radius = cwin.get_double("Radius: ");

    if (radius > 5.0 )
    {   Circle c1 = Circle(Point(0,0), radius - 5.0);
        cwin << c1;
    }

    Circle c2 = Circle(Point(0,0), radius);
    cwin << c2;
    return 0;
}

R2. Relations and Relational Operators

The relational operators in C++ are == != < > <= and >=

x is positive
x is zero or negative
x is at least 10
x is less than 10
x and y are both zero
The last name of e starts with the letter H
The salary of e is at least $50,000
Harry is at least 18 years old.
Harry was born in January.
Harry was born in a leap year (assume his birthday was between 1901 and 2099).

P1. Input validation

#include <iostream>
using namespace std;
#include "ccc_shap.cpp"
main()
{  double slope;

   double xcoord, ycoord;
   Point p1, p2; 

   cout << "Input x coordinate of the first point" << "\n";
   cin >> xcoord;
   cout << "Input y coordinate of the first point" << "\n";
   cin >> ycoord;

   p1 = Point(xcoord, ycoord);

   cout << "Input x coordinate of the second point" << "\n";
   cin >> xcoord;
   cout << "Input y coordinate of the second point" << "\n";
   cin >> ycoord;

   p2 = Point(xcoord, ycoord);

   slope = (p2.get_y() - p1.get_y()) / (p2.get_x() - p1.get_x() );

   cout << "The slope of the line between Points 1 and 2 is " << slope << "\n";
   return 0;
}


P2. The if/else statement

In the previous example, your program probably responded to user input by ignoring cases that would result in a divide by zero. Instead, you can use the if/else format to explicitly specify the action to be taken.

if (test_expression)
   /* do something ... */
else
   /* do something different ... */

A wholesaler advertises a volume discount on blank CD ROMs of 10 cents/disk for each thousand purchased above 10000. (The regular price is $950.00 per 1000, or 95 cents per disk). Write a program that receives the number of blank CD ROMs in an order, then calculates and displays the total cost.

According to your program, how much will it cost to buy

2000 disks?
15000 disks?
180000 disks?

P3. Multiple alternatives

The if/else decision in the preceding example can be extended to select from more than twp possible outcomes. The if ... else if . . else syntax is used to select exactly one of several possible actions.

if (test expression 1)
   /* do something ... */
else if (test expression 2)
   /* do something different ... */
else
   /* do something generic ...   */

Write a program to compute the cost of a purchase of blank CD ROMs as above, but this time, have there be no discount on the first 10000, 5 cents/disk on the second 10,000, 10 cents/disk over 20,000 and 20 cents/disk on any over 50,000.


P4. Nested Branches

If there are multiple conditions, it can happen that a conditionally executed block contains further decisions. Here is an example.

Extend the following code to test whether two circles - each having a fixed center point and a user-defined radius - are disjoint, overlapping or mutually contained.

Disjoint, Overlapping and Concentric circles
#include "ccc_win.cpp"

int main()
{   double radius1 = cwin.get_double("Radius: ");
    Circle circle1(Point(0,0), radius1);

    double radius2 = cwin.get_double("Radius: ");
    Circle circle2(Point(0,4), radius2);

    cwin << circle1 << circle2;

    /*
    Your work goes here
    */

}


P5. Logical Operations

C++ has three logical operations, and, or and not. These are traditionally written as &&, || and !. Both variants are legal under ANSI C++. We find the former easier to read, but many C++ programmer use the latter out of habit. Feel free to use either form in your answers.

Using these operations, express the following:

x and y are both positive or neither of them is positive.

The following program determines if a particular package is elligible for Unidentified Delivery Service's special Northwest Urban Rate Discount. Simplify the nested branches by using Logical Operations and, or, not wherever possible.

#include <iostream>
#include <string>
using namespace std;
int main()
{  cout << "From Address: ";
   string from_address;
   getline(cin, from_address);
   cout << "From City: ";
   string from_city;
   getline(cin, from_city);
   cout << "From State/Province: ";
   string from_state;   
   getline(cin, from_state);

   cout << "To Address: ";
   string to_address;
   getline(cin, to_address);
   cout << "To City: ";
   string to_city;
   getline(cin, to_city);
   cout << "To State/Province: ";
   string to_state;   
   getline(cin, to_state);

   if (from_state == "OR") 
   {   if (from_address.substr(0,11) != "Rural Route")
          first = true;
       else 
          first = false;
   }
   else if(from_state == "WA") 
   {   if (from_address.substr(0,11) != "Rural Route")
          first = true;
       else 
          first = false;
   }
   else if (from_state == "BC")
   {   if (from_address.substr(0,11) != "Rural Route")
          first = true;
       else 
          first = false;
   }
   else
       first = false;

   if (to_state == "OR") 
   {   if (to_address.substr(0,11) != "Rural Route")
          second = true;
       else 
          second = false;
   }
   else if (to_state== "WA") 
   {   if (to_address.substr(0,11) != "Rural Route")
          second = true;
       else 
          second = false;
   }
   else if to_state == "BC")
   {   if (to_address.substr(0,11) != "Rural Route")
          second = true;
       else 
          second = false;
   }
   else
       second = false;

   if (first and second)
       cout << "Package eligible for Northwest Urban Rate Discount!" << "\n";
   else
       cout << "Package eligible for Standard Rate" << "\n";  

   return 0;
}  


R3. Using Boolean variables

According to the following program, what color is the resulting mixture under the following inputs?

Y N Y
Y Y N
N N N
#include <iostream>
#include <string>
using namespace std;

int main()
{  string mixture;      
   bool red, green, blue;
   string string_bool;

   cout << "Include red in mixture? (y/n) " << "\n";
   cin >> string_bool;
   if (string_bool == "y")
      red = true;
   cout << "Include green in mixture? (y/n) " << "\n";
   cin >> string_bool;
   if (string_bool == "y")
      green = true;
   cout << "Include blue in mixture? (y/n) " << "\n";
   cin >> string_bool;
   if (string_bool == "y")
      blue = true;

   if (not blue and not green)     
      mixture = "RED";
   else if (not red and not blue)     
      mixture = "GREEN";
   else if (not red and not green)     
      mixture = "BLUE";
   else if (red)
   {  if (green or blue)
      {  if (green and blue)
            mixture = "BLACK";
         else if (green) 
            mixture = "YELLOW";
         else
            mixture = "PURPLE";
      }
   }
   else
   {  if (blue and green)
         mixture = "CYAN";
      else
         mixture = "WHITE";
   }
   cout << "Your mixture is " << mixture << "\n";

   return 0;
}

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