# W1292 Useful Randomness

## Introduction

In Swift it is possible to return random numbers within a range as a method. Using .random,will allow you to choose a number within a range. The for loop below demonstrates a range of numbers and random numbers printed each time the loop runs. Below we have demonstrated the randomness applied to an Int.

Int

```for _ in 1...5 {
print(Int.random(in: 1..<50))
}
// Prints "49"
// Prints "32"
// Prints "15"
// Prints "9"
```

As you can see above, .random is highlighted in the correct location of where it should be applied.

The Double

In Swift .random can also be applied to Doubles just like Int previously. It is the same idea, but with a double instead of Int and a different output.

```for _ in 1...5 {
print(Double.random(in: 1..<50))
}
// Prints "49.0"
// Prints "32.0"
// Prints "15.0"
// Prints "9.0"
```

## Pythagorean theory

Pythagorean's theorem is an important concept in Euclidean geometry among the three sides of a right triangle. It states that the area of the square whose side is the hypotenuse (the side opposite the right angle) also known as c is equal to the sum of the areas of the squares on the other two sides. The other two sides are known as a and b, a being the adjacent and b being the opposite. This theorem is often written as a+b=c.

## Trigonometric ratios

Sin and Cos are both concepts of Geometry that tie into Pythagorean's Theorem. Soh-Cah-Toa is a acronym used to remember the formulas to solve simple sin and cos functions, Toa known as tangent will be explained later. Focus on sin and cos for now. Recollect the names of each triangle side which was previous described in the Pythagorean's Theorem before moving on.

Sine(Sin)

• Soh is Sin = opposite(b)/hypotenuse(c)

Cosine(Cos)

• Cah is Cos = adjacent(a)/hypotenuse(c)

Tangent(Toa)

• Toa is Tan = opposite(b)/adjacent(a)

### Applications in Swift

In Swift, you can apply Sine , Cosine ,and Tangent in multiple different ways. In my example, we will start by importing a library; this will allow us to apply the pre-built math formulas, hence the import Foundation. If you are not familiar with swifts libraries, it is ok this will be covered in a future lesson.

```import Foundation
//importing the library, will allow the use of the sin,cos,and tan functions
//Double.pi is a Double since pi has decimals

let sine = sin(90.o * Double.pi / 180)
print("Sine \(sine)")

let cosine = cos(90 * Double.pi / 180)
print("Cosine \(cosine)")

let tangent = tan(90 * Double.pi / 180)
print("Tangent \(tangent)")

//Output:
//Sine 1.0
//Cosine 6.12323399573677e-17
//Tangent 1.63312393531954e+16
```

## Excursions

If you would like to experiment that is great!

• Start by opening the swift REPL by typing in swift as seen below.
john-williams@codermerlin:~\$  swift
• Proceed to import your Foundation.
john-williams@codermerlin:~\$  import Foundation
• Finally, explore this concept on your own to have the best learning experience.
• You can reference my previous for loop and experiment, try changing the line value to have different results.
• Always remember to have fun!

## Background Coming Soon Add section on throwing dart at ¼ of square

The value of π can be calculated by:

1. Randomly throwing "darts" at a unit circle
2. Counting the total number of "darts", N
3. Counting the number of "darts" that fall within the unit circle, C
4. The ratio of the area inside the circle to the total area is C/N
5. The value of π is four times this value (because the area of the total square is 2 units x 2 units)

## Prepare

Create a new directory in your ~/Experiences directory named "W1292". Use emacs to edit a file named "main.swift":

zay-vin@codermerlin:~\$  cd ~/Experiences
zay-vin@codermerlin:~/Experiences\$  mkdir W1292
zay-vin@codermerlin:~/Experiences\$  cd W1292
zay-vin@codermerlin:~/Experiences/project-1292\$  swift-init
zay-vin@codermerlin:~/Experiences/project-1292\$  emacs main.swift Helpful Hint You can run your program from within emacs with F5-r Helpful Hint You can find the square root of a number using the squareRoot function. This function is included in the Foundation library, so it must be imported. For example: ```import Foundation let d = 12.0 print(d.squareRoot()) ``` Observe, Ponder, and Journal Section 1 Complete your program, then answers these questions. Estimate the value of π using your program Throw 100 darts (N = 100). What result do you obtain? Throw 1000 darts (N = 1000). What result do you obtain? How is the second result different from your previous result? How large should N be to accurately estimate π to five digits? How important is it that the dart be "thrown" randomly?

## Exercises Exercises Write a program that randomly throws a series of N darts at a virtual dartboard as described above. At the conclusion of throwing N darts, the program should print an estimate for the value of π. Be sure to complete this part of the exercise in your ~/Experiences/W1292 directory.  J1292  Create a journal and answer all questions in this experience. Be sure to include all sections of the journal, properly formatted.

## Key Concepts Key Concepts Random numbers meet the following two criteria: Even distribution over a defined interval Impossible to predict subsequent values based upon previous values Random numbers can be very useful in certain circumstances

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