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JavaScript Numbers

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Random Number Challenge – Two Numbers Solution

4:06 with Guil Hernandez

Update the random number program to ask for two numbers, then provide a random number between the two.

What if the value of lowNumber is 0?

The number zero is considered a "falsy" value in JavaScript. In other words, if the value of lowerNumber is 0, the if condition evaluates to false, and the code in the else clause runs.

To make the number 0 an acceptable lowNumber value in the random number program, use the 'greater than or equal tooperator (>=`) in the condition:

if ( lowNumber >= 0 && highNumber ) {
  ...
} else {
  ...
}

Another approach using isNaN()

JavaScript provides a special function called isNaN() (or "is not a number") that takes one argument and returns a boolean value. It returns true if the value is NOT a number, and false if it is.

For example, passing the string 'six' to isNaN() returns the value true. However, passing it an actual number, like 6, returns false.

In this case, you first test if EITHER variable is not a number. If even one is not a number, display the "Try again" message. To test both variables, use the logical OR (||) operator:

// Convert the input to a number
const lowNumber = parseInt(inputLow);
const highNumber = parseInt(inputHigh);

// Check if lowNumber OR highNumber is not a number
if ( isNaN(lowNumber) || isNaN(highNumber) ) {
  console.log('You need to provide two numbers. Try again.');
} else {
  // Use Math.random() and the user's number to generate a random number
  const randomNumber = Math.floor( Math.random() * (highNumber - lowNumber + 1) ) + lowNumber;

  // Create a message displaying the random number
  console.log(`${randomNumber} is a random number between ${lowNumber} and ${highNumber}.`);
}

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    All right now I will show you how I solved the second part of this challenge. 0:00
    The program should ask for two numbers and provide a random number between the two. 0:04
    First, I need to ask for another input. 0:09
    I will declare a variable named inputLow and assign it the prompt method. 0:11
    I'll pass it the string "Please provide your lowest number". 0:18
    Then change the input high message to Please provide your highest number. 0:25
    The string value stored and input low needs to be converted into a number type. 0:33
    I'll store that number value in a variable named lowNumber. 0:39
    I'll again use the parseInt method to convert the string to an integer. 0:44
    The variable lowNumber represents the lowest possible random number. 0:53
    So now I need to change how the random number gets generated. 0:58
    For example, instead of being a number from 1 to the value stored in highNumber, 1:01
    it needs to generate a number from lowNumber to highNumber. 1:07
    To achieve this, I'll change the number being multiplied by Math.random. 1:11
    I'll subtract the lowNumber from the highNumber and 1:16
    add 1 to it with highNumber- lowNumber + 1. 1:21
    And then add the lowNumber to the return value of Math.floor. 1:26
    So this generates a number from 0 to the difference between the highest and 1:34
    lowest number plus 1. 1:39
    For example, if I want a random number from 10 to 25. 1:41
    Well, 25 minus 10 plus 1 is 16. 1:45
    So this would generate a random number from 0 up to but not including 16. 1:50
    By providing that value to Math.floor, I'll get a random number from 0 to 15. 1:56
    Then, I add the lowest number which produces the number from 10 to 25. 2:02
    Now, don't worry at all if the math still seems confusing. 2:07
    At least now you have an equation that does the math for you. 2:10
    Next, I'll update the random number console message by inserting the value of 2:14
    the low number variable into the string. 2:18
    And I'll update the message in the else clause to You need to provide two numbers. 2:25
    Try again. 2:30
    Finally, I'll update the condition and the if statement. 2:34
    This time I need to check if the values stored in lowNumber and 2:38
    the value in highNumber is a true number. 2:43
    In other words, make sure that both are not NaN or not a number. 2:46
    I'll use the logical and operator, 2:50
    you learned about in a previous course in the condition like this. 2:52
    lowNumber && highNumber. 2:56
    If even one of these is not a number, 3:00
    the entire condition evaluates to false and the code in the else clause runs. 3:03
    Okay, let's see how this works now. 3:09
    I'll save my file, refresh the page. 3:12
    I'll enter the lowest number, let's say 10 and the highest number 25. 3:15
    The console outputs the message 14 is a random number between 10 and 25. 3:22
    Now, I'll try entering a value like three then 15. 3:28
    The console outputs, You need to provide two numbers. 3:34
    Try again, good. 3:37
    Nice work with the addition of numeric data types and 3:42
    the Math object to your toolset, 3:44
    you're well on your way to programming some pretty powerful applications. 3:46
    To practice more with numbers and math, 3:51
    be sure to review the resources posted in the teacher's notes. 3:53
    And we're here to help. 3:56
    So if you have questions about anything covered in this course, 3:57
    feel free to reach out to other students in the community or the treehouse staff. 4:00
    Thanks everyone and happy coding. 4:04

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