%= assignment operator

Question

x=2
x%=4 (or x%=6, or x%=7 etc.)
output: always 2
why? why it always gives as output the default value which assigned to x.

Answer 1

it means when we can't divide first value to another, then we must multiple 0 to dividible value, and plus the first value, yes?

Answer 2

thanks a lot Kishalaya, I understand what you wrote in all comments, but still blur for me why? I think this rule must rely to something in the math.

Answer 3

because you will get a decimal result and not the modulus, the modulus result of any operation like num%numbigger is always num

Answer 4

tardigrade
That "something" in math is called Euclidean division: https://en.m.wikipedia.org/wiki/Euclidean_division

Note the statement: "Given two integers a and b, with b ≠ 0, there exist unique integers q and r such that
a = bq + r
and
0 ≤ r < |b|,
where |b| denotes the absolute value of b.
The four integers that appear in this theorem have been given names: a is called the dividend, b is called the divisor, q is called the quotient and r is called the remainder."

Here we are given a=2 and b=4.

We obtain q=0 and r=2, since they satisfy those two equations, and *must* be unique.

Answer 5

I didn't understand 2=0*4+2. why multiple 0 to 4?

Answer 6

if this is a rule which we must obey, where I can find about it? Google gives nothing )

Answer 7

a %= b is equival to a = a%b. The operation a%b produces the remainder of a when divided by b. For example,
25%3 = 1 (because 25 = 8*3 + 1)
17%5 = 2 (because 17 = 3*5 + 2)
12%4 = 0 (because 12 = 3*4 + 0)

Here x was initally 2, and 2%4=2 (because 2=0*4+2), thus x%=4 gives you 2 for x.

If, instead, you change the first line to x = 15, you'll see that after the second line x becomes 3.

Hope that makes sense :)

Answer 8

because you "can not" divide 2 by 4 with modulus

Answer 9

Yes, I think, Maths experts come here please ;)

Answer 10

tardigrade:
Let me go back to why 25%3 = 1. Here we find the largest multiple of 3 that is not bigger than 25. That multiple is 24 (because 8*3=24, and 9*3=27, which is bigger). Now we do 25-24 and get 1, our remainder.

Same for 2%4. The largest multiple of 4 that is not bigger than 2 is 0 (since 0*4=0, and 1*4=4, which is bigger than 2). Now we do 2-0 to get 2.

Answer 11

because when you say
x%= 4 you mean
x = x%4;

so
2%4 = 2
2%5 =2
2%6=2
2%7=2
2%8=2
2%9=2

to understand easily look at the following
2 divided by 4 equals 0 with a remainder of 2.
2 divided by 5 equals 0 with a remainder of 2.
2 divided by 6 equals 0 with a remainder of 2.
2 divided by 7 equals 0 with a remainder of 2.
2 divided by 8 equals 0 with a remainder of 2.

Therefore, 2%4 evaluates to 2.