How to fix if statements for my rock paper lizard spock program?

Question

Alright, new to coding here, but in my JavaScript program I am attempting to add 2 new conditions to the already popular RPS game (Lizard and Spock). However, when adding these two new conditions in the index.js file, nothing seems to happen.

I've tried changing up the math to .20 each but that did not seem to do anything. I believe that the problem is that I am using the wrong function for 5 different variables (if, else if)

function run() {
    playerChoice = this.innerText;
    computerGamble();
    compare();
}

function computerGamble() {
    var dice = Math.random();
    if (dice <= 0.33) {
        computerChoice = "Rock";
    } else if (dice > 0.33 && dice <= 0.66) {
        computerChoice = "Paper";
    } else {
        computerChoice = "Scissors";
    } else {
      computerChoice = "Lizard";
    } else {
      computerChoice = "Spock";
    }
}

All variables/conditions should have an equal chance to be picked.

Answer 1

Basically you have like other pointed out as well use if else statements and divide it by number of choices.

function computerGamble() {
    var dice = Math.random();
    if (dice < 0.2) {
        computerChoice = "Rock";
    } else if (dice < 0.4) {
        computerChoice = "Paper";
    } else if (dice < 0.6) {
        computerChoice = "Scissors";
    } else if (dice < 0.8) {
      computerChoice = "Lizard";
    } else{
      computerChoice = "Spock";
}

As an alternative I think I would just use random-numbers between 0-5 and than use a simple switch case statement like so:

function run() {
    playerChoice = this.innerText;
    computerGamble();
    compare();
}

let numberOfChoices = 5;
function computerGamble() {
 var dice = Math.floor(Math.random()*numberOfChoices); //numbers between 0-5
 switch(dice){
  case 1: computerChoice = "Rock";break;
  case 2: computerChoice = "Paper";break;
  case 3: computerChoice = "Scissors";break;
  case 4: computerChoice = "Lizard";break;
  case 5: computerChoice = "Spock";break;
 }
}

Than you can easily adjust the number of choices and don't have to deal with some hard coded decimal numbers if you want to change something. And personally I think its a bit more clear in a switch case - it looks a bit more tidied up. Or without any statements:

let numberOfChoices = 4;
function computerGamble() {
 let choices = ["Rock", "Paper", "Scissors", "Lizard", "Spock"];
 var dice = Math.floor(Math.random()*numberOfChoices); //numbers between 0-4
 computerChoice = choices[dice];
}

Answer 2

You need to add else if for every outcome. i.e you should have something more like

function computerGamble() {
    var dice = Math.random();
    if (dice <= 0.2) {
        computerChoice = "Rock";
    } else if (dice <= 0.4) {
        computerChoice = "Paper";
    } else if (dice <= 0.6) {
        computerChoice = "Scissors";
    } else if (dice <= 0.8) {
      computerChoice = "Lizard";
    } else{
      computerChoice = "Spock";
}

---

also regarding your statement else if (dice > 0.33 && dice <= 0.66) each else implies that the one before it didn't occur so if dice was 0.25 then the first if would evaluate to false and the second else if would be attempted. If on the other hand dice was 0.1 then only the statement in the first if would execute an all of the other elses would be skipped. as a result you don't need to compare with the lower bound again as it already implicitly satisfies that condition.

Answer 3

With an IF statement, you can have any number of "else if" you need, but only one final else, meaning that if the previous possibilities fail, this is the path to execute. So, you'll need to modify your example to something like:

if (dice <= 0.20) {
  computerChoice = "Rock";
} else if (dice > 0.20 && dice <= 0.40) {
  computerChoice = "Paper";
} else if (dice > 0.40 && dice <= 0.60) {
  computerChoice = "Scissors";
} else if (dice > 0.60 && dice <= 0.80) {
  computerChoice = "Lizard";
} else {
  computerChoice = "Spock";
}

Answer 4

Here's a completely automated solution for your problem:

If you wish to have a random option out of an arbitrary Array of values, in an automated way, where your function does not care or know in advance about the number of options, then you can use a bit of math and place it inside an iterator.

The main line of thought in these situations is to go from your maximum value down to the lowest, and this will be tremendously helpful with your if..else statements because it eliminate the need to check if the current value is within a range. All you need to do is just test if the current value is equal or below a certain threshold, but not within a range.

// dice-roller on fixed input Array
const randomOption = options => () => options[Math.floor(Math.random() * options.length)]

// initiailze "randomOption" with an Array of possible values
const getRandomOption = randomOption(["Spock", "Lizard", "Scissors", "Paper", "Rock"])

// roll the dice 10 times
for( let i = 10; i--; )
  console.log(  getRandomOption()  )