learngo/13-loops/questions/02-randomization.md

What's pseudorandom number generation?

1. Numbers appear to be randomly generated but in reality they are not CORRECT
2. Generating random numbers according to the physical laws
3. Generating pseudo even and odd numbers

1: Computers are deterministic machines. They can't generate truly random numbers (unlike actual physical processes).

What's a seed number?

1. Exchanging of random numbers between two computers
2. It's used to getting a random number between 0 and the seed number
3. It's used initialize a pseduorandom number generator CORRECT

Which package is used to generate pseudorandom numbers in Go?

1. pseudorand
2. rand CORRECT
3. random
4. randomizer

What does [0, 5) mean?

1. A range of numbers between 0 and 5 (excluding 5) CORRECT
2. A range of numbers between 0 and 5 (including 5)
3. Just 0 and 5
4. Just 0 and 4

1: Right. The square-brace means: "inclusion". The parenthesis means: "exclusion". So, [0, 5] means: 0, 1, 2, 3, 4. It's called the "mathematical interval notation".

Why this function call would not work?

rand.Intn(0)

1. First you should seed it
2. It expects two arguments
3. Intn works within a range of [0, 0). So, it doesn't make sense to include 0 and not include 0 at the same time. CORRECT

1: That's not the cause of this error. You don't always have to seed it. 2: No, it does not.

What does this program print?

Note that, each seed number below returns pseudorandom numbers as these:

Seed: 0
  3 3 6 8 4 1 9 3 6 6

Seed: 1
  1 1 9 3 2 4 7 6 6 6

Seed: 2
  10 1 2 2 0 6 4 1 0 5

Here's the program:

package main

import (
	"fmt"
	"math/rand"
)

func main() {
	for i := 0; i < 3; i++ {
		rand.Seed(int64(i))
		fmt.Print(rand.Intn(11), " ")
		fmt.Print(rand.Intn(11), " ")
	}
}

1. 3 1 10 3 1 1
2. 3 6 1 6 10 5
3. 1 10 1 1 3 3
4. 3 3 1 1 10 1 CORRECT

4: The numbers are determined depending on the seed number. So, this loop, seeds the pseudorandom generator with 0, 1, and 2 respectively.

And, after each seed, it calls Intn twice to generate two random numbers.

So, if you look at the result, 3 3 is the first two numbers of Seed: 0. 1 1 for Seed: 1. And, 10 1 for Seed: 2.

What you should do if you want the pseudorandom generator to produce random numbers each time you run your program?

1. You need to seed it like this: rand.Seed(rand.Random)
2. You need to seed it like this: rand.Seed(time.Now().UnixNano()) CORRECT
3. You need to seed it like this: rand.Seed(time.Now())