C++ Activity

Lab Objectives

To gain experience in

• implementing simple decisions
• writing expressions with relational operators
• input validation
• simple loops
• using Boolean variables

---

R1. The if statement

In C++, decisions to execute or not execute a statement or group of statements can be made by using the statement if (condition). The condition 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.
In the example below:
How much money will be added to your account when the initial starting amount is $100?
How much money will be added to your account when the initial starting amount is $85?

#include 

int main()
{ 
    
    
double initial_value, final_value;
cout <<"Please enter the initial balance: ";
cin >> initial_value;
if (inital_value > 90 )
    {  
final_value = final_value + 10;
}

    final_value = final_value + 5;
    cout <<"Final Value" <

    
    

    
    
R2. Relations and Relational Operators
The relational operators in C++ are  == != < > <= and >=
Formulate the following conditions in C++: 

         
x is positive
         
       
         
x is zero or negative
         
       
         
x is at least 8
         
       
         
x is less than 8
         
       
         
x and y are both zero
         
       
Formulate the following conditions for the employee object e.

         
The last name of e starts with the letter H
         
       
         
The salary of e is at least $75,000
         
       
Formulate the following conditions on the variable harrys_birthday of type Time.
    

         
Harry is at least 21 years old.
         
       
         
Harry was born in August.
         
       
         
Harry was born in a leap year (assume his birthday was between 1901         and 2099).
         
       

    
    
P1. Input validation
Build and run the following program. Describe what happens when the two points have the same x coordinate?
    
    
#include 
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;
}
Correct and rebuild the program to disallow a vertical line
        (denominator = 0).
    
    
/* paste program here */
What are the results when point1=(4,2) and point2 = (4,2) ?

What are the results when when point1=(4,2.5) and point2 = (3,1.5) ?



    
P2. Additional Input Validation Exercise
Build and run the following program. Describe what happens when
    the salaries from the first and second years are equal.
    
    
#include 
    using namespace std;
    int main()
    { 
   double fyear_sal, syear_sal,tyear_sal;

   cout << "Input the first year's salary:" << "\n";
   cin >> fyear_sal;;
   cout <<  "Input the second year's salary:" <<  "\n";
   cin >> syear_sal;
   cout << "Input the third year's salary:" << "\n";
   cin >> tyear_sal;
   cout <<  "The difference between the third and second year salary and second and first is:"
   cout << ((tyear_sal-syear_sal)/(syear_sal-fyear_sal))*100 << "%";
   return 0;
    }
    
Correct and rebuild the program to not allow for case where both
        the first and second year salaries are the same.
    

What are the results when fyear_salary = 100000 and syear_salary =
        100000?
    

    
    
P3. The if/else Statement
In the previous examples, 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 (condition)
   /* do something ... */
else
   /* do something different ... */
The electric company gives a discount on electricity based upon
    usage. The normal rate is $.60 per Kilowatt Hour (KWH). If the
    number of KWH is above 1,000, then the rate is $.45 per KWH. Write a
    program that prompts the user for the number of Kilowatt Hours used and then
    calculates and prints the total electric bill. 

/* paste program here */
According to your program, how much will it cost for:

         
900 KWH?
         
       
         
1,754 KWH?
         
       
         
10,000 KWH?
         
       

    
    
P4. Simple Loops
Frequently a decision needs to be made whether or not to do something
      again. Here is a program that computes the number of digits needed to
      represent a number in base 10, just like the function digits()
      from the preceding lab. But instead of using recursion it uses multiple
      if statements. 
/* PURPOSE:  Count number of digits needed to express an integer in base 10
             using multiple if statements
   REMARKS:  Compare to Ch.5 digits()
*/

#include 
using namespace std;

int main()
{  int input;

   cout << "Input an integer between 1 and 9999: ";
   cin >> input;

   int temp = input;
   int d = 1;

   assert ( input >= 1 and input <= 9999 );
    
   if (temp > 9)
   {  temp = temp / 10;
      d++;
   }
      
   if (temp > 9)
   {  temp = temp / 10;
      d++;
   }

   if (temp > 9)
   {  temp = temp / 10;
      d++;
   }

   if (temp > 9)
   {  temp = temp / 10;
      d++;
   }
   
   cout << input << " can be expressed in " << d << " digits" << "\n";
   
   return 0;
}

But having to write
if (temp > 9)
   {   temp = temp / 10;
       d++;
   }
four times, even using copy/paste, is clearly repetitive! It also only
      works for input <= 9999. One would like to have a way of testing that
      the input is still greater than 1 and executing the succeeding control
      block if it is. Replacing  if  with  while  does it.
    
/* PURPOSE:  Count number of digits needed to express an integer in base 10
             using while loop
*/

#include 
using namespace std;

int main()
{  int input;
  
   cout << "Input an integer: ";
   cin >> input;
   int d = 1;
   int temp = input;

   while (temp > 9)
   {  temp = temp / 10;
      d++;
   }

   cout << input << " can be expressed in " << d << " digits" << "\n";   
}
The fractions 1/2, 1/4, 1/8, ... get closer and closer to 0. Change the
      previous program to count the number of divisions by two needed to be
      within 0.0001 of zero.
/* paste program here */
    


    
P5. Loop Termination
Which values of nyear cause the following loops to terminate?
/* PURPOSE: Count number of year between a user-input year and the
            year 2000.
*/            

int main()
{  int nyear;
   millennium = 2000;
   
   cout << "Please enter the current year";
   cin >> nyear;
   
   while (nyear != millennium)
   {  nyear++;
   }
   
   cout << " Another "<< millenium - nyear << "years to the millenium." << "\n";
   return 0;
}
   

    
    Re-write the preceding program so that the while loop will terminate for
      any integer input.
/* paste program here */
    
    
    


    
    
P6. Processing a Sequence of Inputs
Modify the electricity rate program to allow the user to enter data for any
    number of months.  The user should be able to enter a -1 when
    finished. The program should then compute the cost using the same
    formulas as above.
/* paste program here */

    
    
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 
#include 
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;
}