15110 SUMMER SESSION ONE - 2013

Lab 2 - Wednesday, May 22

Deliverables

1. force.rb (demonstration)
2. circle_area.rb (demonstration)
3. answers.txt
4. sphere_vol.rb
5. factorial.rb

Place these files in a lab2 folder. Before leaving lab, zip up this folder, and hand it in.

CA Demonstration

• creating a lab2 directory
• starting irb within a terminal window
• math constants and print: circle_area(r) to calculate \(A = \pi r^2 \)
  • Math.sqrt(x) and Math::PI
  • returning a value from circle_area(r)
  • using the return value
  • printing a value instead of returning
• creating a simple function that computes and returns the sum 1+ 2 + ... + n for positive integer n using a loop.

Activities

1. Type each of the following expressions into irb. What value do each of the following Ruby expressions evaluate to? Is that value an integer or a floating point?

   1. 250
   2. 28 % 5
   3. 2.5e2
   4. 3e5
   5. 3 * 10**5
   6. 20 + 35 * 2
      Why is this different from (20 + 35) * 2?
   7. 3.0 * 2 / 3
   8. 2 / 3 * 3.0
      Why is this different from 3.0 * 2 / 3?
   9. 25 - 5 * 2 - 9
      Is this different from ((25 - 5) * 2) - 9 and/or 25 - ((5 * 2) - 9)? Why?

   Write your answers in the file answers.txt. (Review Unit 2A lecture slides if necessary.)

2. In sphere_vol.rb, define a Ruby function sphere_vol(r) that calculates and returns the volume of a sphere with a radius r. This can be calculated using the formula:

   \[ V = \frac{4}{3}\pi r^3\]

   Place in answers.txt a copy of irb lines in which you call sphere_vol(r) to compute the volume of sphere with a radius of 7 and irb shows you the result.

3. In factorial.rb, define a Ruby function factorial(n) that calculates and returns n! = (1)*(2)*...*(n-1)*(n). You may assume that n is greater than or equal to 1 for this problem. HINT: You will need a variable to hold the result, initially set at 1. (Why?) Then your loop should multiply into this variable each value from 1 up to n.

   Place in answers.txt a copy of irb lines in which you call factorial(n) to compute 4!, 10! and 26! and irb shows you the result each time.