Being able to manipulate numbers and perform mathematical operations is an essential skill in JavaScript. In fact, it’s almost unavoidable! Whether it’s converting ingredients from cups to tablespoons in a baking program, or having a counter in a video game that keeps track of a user’s high score, or placing graphic elements on a webpage, math is everywhere.
The nice thing about the math in JavaScript is that we approach it exactly the same way we would if we were doing it by hand or with a calculator. For example, in the program below, we are performing very simple calculations. Run the program to see their results.
In the example above, try changing the calculations to something more complex. You can use any of the below mathematical operation symbols in JavaScript.
+ for Addition
- for Subtraction
/ for Division
* for Multiplication
** for Exponent
Remember PEMDAS from Algebra?? The same rules apply to JavaScript as well: the operations in a calculation will follow the order of Parentheses, then Exponents, then Multiplication and Division, then Addition and Subtraction. Test your PEMDAS skills in the following two questions:
Choose the correct output of the code: println(5 + 7 - 2 * 2).
Choose the correct output of the code: println(110 / 10 - (2 + 3)).
Now in programming, we often use both numbers and variables (that store numbers)! We perform the math operations the same way with variables as we do with numbers.Take a look at the following program that converts a user inputted temperature in Fahrenheit to Celsius. As you run the program, consider the questions below:
Math.round(celsius) is a function that rounds the number stored in celsius to the nearest integer, storing the new value in celsiusRounded. Try deleting that function to see how it changes the program’s output (that is, make line 8 read: celsiusRounded = celsius).There is one other mathematical operation in JavaScript that is super useful:
% for Modulus
If you are new to programming, you probably haven’t seen this before. It can be a little tricky at first. Take a look at the example below and see if you can figure out what the modulus calculation is storing in the variables. Try inputing your own modulus calculations to explore further.
Were you able to figure it out??
Answer: the Modulus operator divides the two numbers, then keeps the remainder. Look again at the above calculations. Do you see it now?
15 / 6 = 2 with a remainder of 3
15 / 5 = 3 with a remainder of 0
15 / 4 = 3 with a remainder of 3
15 / 3 = 5 with a remainder of 0
15 / 2 = 7 with a remainder of 1
The remainder is what’s kept in the modulus calculation. This can be very useful in programs! For example, if you want to determine if a number is even, you can write following code: var remainder = number % 2. If the variable remainder is equal to 0, then number is even (since there was no remainder)!
Imagine a scenario where you are hosting a holiday party for your friends, and you are paying a company to cater the food. They charge $50 per table that can hold up to 5 people (or $10 per person). If there are any extra people that don’t fit at a full 5 person table, they can sit at an extra table that costs $15 per extra person (this catering company discourages partially full tables by charging more per person).
For example, if 23 people attend the party, there will be four full tables with 5 people each (a total of 20), and one extra table with 3 people. The total cost would be (4x50) + (3x15) = $245.
In the editor below, write a program that does the following:
HINTS:
TEST CASES:
There are many situations in which we only want to perform a very simple calculation. For example, an adventure video game might want to keep track of how many items the player is carrying. Every time the player picks up or drops an item, the variable containing the item count needs to increase or decrease by 1.
Instead of writing itemCount = itemCount + 1 every time, we can actually just write itemCount += 1 or itemCount++. All three of these do the same thing! Take a look at the example below to see some of the different ways you can use this for many simple calculations.
