Exercise Wednesday

## Whiteboard Practice

When and how whiteboarding practice is implemented will be up to your teacher. Below is a recommended prompt.

### Goal

For this section's whiteboarding lesson, we’ll continue to practice with arrays, looping, and using C#'s basic operators (`+`, `-`, `*`, `/`, `%`)

As the interviewee:

• Keep talking.
• Explain your plan at the beginning; recap what you’ve done at the end.
• Make eye contact.

As the interviewer:

• Answer questions as best as you can.
• Be encouraging. Whiteboarding is difficult!
• Be patient. Only offer hints if your partner indicates that they need help.
• Be engaged. Part of this practice is getting used to having someone evaluate your work as your produce it.
• Offer constructive feedback. Find at least one thing that your partner did well and one thing they could improve at.

### Problem

1st Prompt: Write a method that returns a boolean indicating whether a number is prime. Recall that a number is prime if it is greater than 1 and is not evenly divisible by any other numbers excepting 1 and itself.

Examples:

• Given: 7, Output: true

• Given: 2, Output: true

• Given: 8, Output: false

2nd Prompt: Write a method that returns an array of all of the multiples for a given number. A multiple of a given number is a number that can be multiplied by a second number to make the given number.

Examples:

• Given: 7, Output: [ 1, 7 ]

• Given: 24, Output: [ 1, 2, 3, 4, 6, 8, 12, 24 ]

### Further Exploration

• Write a method that returns an array of all the prime numbers that are less than a given number.

• Examples:
• Given: 7, Output: [ 2, 3, 5 ]
• Given: 2, Output: [ ]
• Write a method that returns the greatest common multiple (GCM) for two given numbers. The GCM is the largest number that both given numbers are evenly divisible by.

• Examples:
• Given: 24, 18, Output: 6
• Given: 50, 8, Output: 2
• Given: 25, 5, Output: 5