FAQ: PHP Numbers - Order of Operations

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This community-built FAQ covers the “Order of Operations” exercise from the lesson “PHP Numbers”.

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FAQs on the exercise Order of Operations

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[cecilelebleu]

Hi!
In this lesson, the order of operators is described, but the Modulo operator (%) isn’t mentioned. The order explained is:

1. ()
2. **
3. * and /
4. + and -

I suppose the modulo operator is at number 2, next to exponentiation, but want to make sure.

Thanks!

[midlindner]

It’s actually at number 3 on your list. It’s basically treated like / but returns the remainder instead of the quotient.

[cecilelebleu]

Ok, thank you for clearing that out!

[mtf]

Definitely bookmark this page for easy reference. Until this stuff is cemented in our minds, it can never hurt to double check.

PHP: Operator Precedence - Manual

When two operators have equal precedence, association is left to right. This can have a bearing on the result so order of placement becomes the precedence determiner.

 > 10 % 3 / 4
<- 0.25
 > 10 / 4 % 3
<- 2.5
 > 10 % 3 * 4
<- 4
 > 10 * 4 % 3
<- 1
 > 

Times and powers are not equal precedence so can be written however they occur without changing the result.

 > 2 ** 2 * 4
<- 16
 > 4 * 2 ** 2
<- 16
 > 

---

Totally off topic and different language, but the gist is the same.

>>> list(map(lambda x: 10 / x % 3, range(1, 10)))
[1.0, 2.0, 0.3333333333333335, 2.5, 2.0, 1.6666666666666667, 1.4285714285714286, 1.25, 1.1111111111111112]
>>> list(map(lambda x: 10 % 3 / x, range(1, 10)))
[1.0, 0.5, 0.3333333333333333, 0.25, 0.2, 0.16666666666666666, 0.14285714285714285, 0.125, 0.1111111111111111]
>>> 

Note the relationship between corresponding terms in each list. I’d love to see these two graphs plotted if there are any matplotlib savvy learners. Apologize for bringing Python into the mix, but it is more for convenience. The point is the relation between these two graphs, which is what I found kind of interesting, nothing to do with the OP, save the illustration of precendence with two curves.

[radeakanta]

94 - 4.25 + 7 - (23.50 + 23.50 * .2) + 20 / 4;

Why do we have to * .2 on (23.50 + 23.50 * .2)? What is the meaning of .2?

[zunaid.hassan]

@radeakanta

0.2 is the result of 20%(=20/100=0.2).

From the exercise:

• I went out for a meal. The bill was $23.50, but I also gave a 20% tip.

Since the % symbol is reserved for the Module operator, I believe we cannot use it to show percentage.

So,
20% of $23.50
= 0.2 * 23.50
= $4.70.

[core5118577814]

I think the solution is pretty unfair in my opinion, since the the exercise is not using the same method that’s been shown on the example, the PEMDAS really not implemented, you can’t just have

I went out for a meal. The bill was $23.50, but I also gave a 20% tip.

and make the 20% as a direct 1.2, we should count it first, or at least you could make that part as the parentheses ones or something so that would be good maybe like (23.50 * (20 / 100))…you know something like that