1. UMBC CMSC 104 – Section 01, Fall 2016
Algorithms III

2. Notes & Announcements Project 2 due… now! Project 3 posted tonight
Due next Thursday 10/13 at 5:30 PM

3. Writing Algorithms from Scratch
Given a problem statement, we are going to write the corresponding generic algorithm for the solution.
We will use the following procedure:
Determine the algorithm inputs and outputs
Pseudocode a rough algorithm
Complete the pseudocode

4. The Cube
Problem: Write an interactive program to compute and display the volume and surface area of a cube. The program must also display the cube dimensions. Error checking should be done to be sure that all cube dimensions are greater than zero.

5. The Cube: What Do We Know?
We’re working with a cube.
Cubes have equal length sides.
Lets call our side length x.
We need to calculate surface area of the cube.
Cubes have 6 sides.
6x2
We need to calculate the volume of the cube. x3
We need to display the cube dimensions
We need to verify that all dimensions are greater than zero

6. The Cube: Inputs & Outputs
Side length
Outputs
Dimensions
Surface Area
Volume

7. The Cube: Rough Pseudocode
Display “Enter the side length” Read <length> <surface area> = 6 * <length> * <length> <volume> = <length> * <length> * <length> Display “The dimensions are <length> x <length> x <length>” Display “The surface area is <surface area>” Display “The volume is <volume>”

8. The Cube: What are we missing?
We’ve met all of our requirements, except ensuring all side lengths are greater than zero.
How might we do this?

9. Control Structures
Any problem can be solved using only three logical control structures:
Sequence
Selection
Repetition

10. The Cube: Final Pseudocode
Display “Enter the side length”
Read <length>
If (<length> is less than 1)
Display “Invalid length! I quit!”
Else
<surface area> = 6 * <length> * <length>
<volume> = <length> * <length> * <length>
Display “The dimensions are <length> x <length> x <length>”
Display “The surface area is <surface area>” Display “The volume is <volume>”
End_If

11. The Cube: Final Pseudocode
Display “Enter the side length” Read <length> While (<length> is less than 1) Display “Invalid length! Try again!” End_While <surface area> = 6 * <length> * <length> <volume> = <length> * <length> * <length> Display “The dimensions are <length> x <length> x <length>” Display “The surface area is <surface area>” Display “The volume is <volume>”

12. Drawing a Rectangle
Problem: Write an interactive program that will draw a solid rectangle of asterisks (*). The program begins by prompting for dimensions. Error checking must be done to be sure that the dimensions are greater than zero.

13. A Solution…
Display “Enter length” Read <length> Display “Enter width” Read <width> <length count> = 0 <width count> = 0 While (<length count> < <length>) While (<width count> < <width>) Display “*” <width count> = <width count> + 1 End_While Display Newline <length count> = <length count> + 1

14. Questions?