Lab Conditional Statements Part 2

Conditional Practice, Continued

Consider this example from your textbook page 30:

   $roll = rand(1, 6);
   
   echo "You rolled a $roll";
   if ($roll == 6) {
      echo "You win this round!";
   }
   else {
      echo "Sorry, you didn't win this round, better luck next time!";
   }
   
   echo "Thanks for playing";

1. Let's change the game in the following way:

   • Add variable $points and assign it a starting value of 10
   • If the player rolls a 6, add five to the value of $points
   • If they do not roll a 6, take away three from the value of $points
   • Either way, announce the player's score after their turn.

Nested Conditional Statements

Below we have an example of nested conditional statements:

   $grades = rand(40,100);

   if($grades >= 60){
      if($grades >= 90){
         echo "Congratulations! You Aced it!";
      }
      else{
         echo "You passed";
      }
   }
   else {
      echo "See me after class";
   }

2. Describe how the program will run when $grades has the value of 87.

3. Expand upon this snippet of code to have it output different messages for letter grades A-D using conditional statements with the cutoffs: 60, 70, 80, 90.

4. Based on your past experience with forms,

   1. Write your own form page that reports three names ($nameOne, $nameTwo, $nameThree).
   2. Now write a conditional statement that takes the data from this form and prints the names in alphabetical order.
   3. Review your work, in the case that two (or all three) of the names are the same.

Triangles

Refresher from geometry: In order for three numbers to identify the length of sides in a triangle, the sum of any two must be greater than the third:

   a + b > c
   a + c > c
   b + c > a

Below is a refresher of this concept.

EXAMPLES:

Example A: Consider

• $a = 4;
• $b = 6;
• $c = 4;

For these values, each of the triangle equations are satisfied, so this is a triangle.

Example B: Consider

• $a = 3;
• $b = 7;
• $c = 15;

Here, it is not true that $a + $b > $c, so this is not a triangle.

5. With this background, write a program to determine whether or not a triangle can be formed , given three sides.

   • Assign random values to three variables:

        $a = rand(2,20);
        $b = rand(2,20);
        $c = rand(2,20);
     

   • If a triangle can be formed, determine if it is equilateral (all sides equal length), isosceles (two equal sides lengths) or scalene (all different sized sides).
   • If the sides do not form a triangle, report that conclusion.

Logical Operators

We have some other operators that help us use more complex conditions.

Examples

Some Illustrious Applications

Driver's insurance can be pricey, especially for young people. Fortunately for college-age students, each year it gets cheaper until your mid 30's, and insurers also offer 'good grades' discounts.

The table below lists some fictional insurance rates based on age:

6. Assume that the average discount for good grades is 18%, so students who qualify pay 82% of the price listed for their age range,

   1. Write a program that contains the following:
      • Variable $insuranceAge that stipulates the age displayed in the chart above
      • Variable $goodGrades that is either true or false based on whether the student qualifies for the discount
      • The logical comparator variable &&
      • Echo the person's premium
   2. Replace the && with ||. What does this do to the program? Why?

7. Checking Prerequisites

   1. In order for students to take the Computer Science thesis class, they must have taken CS-141, CS-241, and be declared as a CS-major. Write a program that prints whether or not a student may register for the thesis, based on these prerequisites:
      • $major is Computer Science
      • $CS141 is true
      • $CS241 is true

      Output might be

          Success! You can register for CS 495W
          

      or

          Sorry, you have not fulfilled the prerequisites for this course
          

   2. ENVS-120, Social Systems and the Environment, is only offered to first-year and second-year students who are environmental science or archaeology majors. Edit your code from part a. in order to fit the new parameters:

      • $major is Environmental Science or Archaeology

      • $class is firstYear or secondYear

RGB Values

In digital photography and on Web pages, pictures are divided into pixels, as discussed in the first reading and lab on cascading style sheets. In this setting, colors are seperated into red, green, and blue values, each in the range from 0 to 255.

(0,0,0) is black, white is (255,255,255), (255,0,0) is pure red etc. Here is a table to help you get an understanding of the kinds of colors you can make:

As you can see, you can customize your color very specifically through using RGB. For more information this website can be helpful:

RGB Chart

With this concept of RGB in mind, we can make each of these three values a variable:

	$red = rand(0,255);
	$green = rand(0,255);
	$blue = rand(0,255);

If we take an example RGB combo (230, 15, 20), its distance from red, rgb(255,0,0), may be found considering the distance of the red, green, and blue values:

	255-100 = 155 (red distance)
	0-15 = -15 (green distance)
	0-20 = -20 (blue distance)

Then these results are squared results and added to get a distance (actually a distance squared): (155)² + (-15)² + (-20)² = 24650

Comparing these computations against red (rgb(255,0,0)), green (rgb(0,255,0)), and blue (rgb(0,0,255)) will indicate what primary color is closest to the given color.

9. Comparing colors:

   1. Write a program that determine which of the following colors is closest to blue.

      1. (10,40,200)

      2. (127, 127, 127)

      3. 255, 10, 200)

   2. Follow a similar approach to determine which of the following is closest to green.

      1. (0, 164, 117)

      2. (89, 190, 82)

      3. (15, 15, 200)

Reflection

10. Both the previous lab and this lab have provided experience with various forms of if statements and conditions.

    Concepts:

    • if statements, if/else statements and elseif statements
    • Nested if statements
    • &&, ||, != operators

    Time for reflection:

    1. To what extent are you comfortable with each of these ideas?
    2. Do all of the ideas seem clear?
    3. Are some confusing? (Please talk to the instructor about any questions!)

created 4 February 2019 by Zhen Zhen McMahon modest editing 9 February 2019 by Zhen Zhen McMahon and Henry M. Walker