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|() Mod ()|
The () Mod () block ("mod" is short for "modulo") is an Operators block and a reporter block. It reports the remainder when the first input is divided by the second. For example, when 10 is put in the first input and 3 in the second, the block will report 1; 10 divided by 3 gives a remainder of 1.
() Mod () supposes the quotient (result of division) is always rounded down, even if it is negative. For example, -10 mod 3 = 2, not -1, because the quotient -10/3 is rounded down to -4, giving a positive remainder.[note 1]
If a project is doing divisibility tests, the () Mod () block can be of use.
Some common uses for the () Mod () block:
- Checking if two numbers divide without a remainder
if <((a) mod (b)) = > then say [a is divisible by b] else say [a is not divisible by b] end
- Checking if a number is a whole number
if <((a) mod (1)) = > then say [a is a whole number] else say [a is not a whole number] end
- Checking if numbers are odd or even
if <((a) mod (2)) = > then say [a is an even number] else if <((a) mod (1)) = > then say [a is an odd number] else say [a is not an integer] end end
- Repeatedly iterating through a list:
when gf clicked set [x v] to  forever change [x v] by (1) say (item (x) of [list v]) set [x v] to ((x) mod (length of [list v])) end
- Reusing background-sprites when scrolling
when gf clicked forever set x to (((x position) + (240)) mod (480)) end
- Main article: List of Block Workarounds
Because the remainder of a division is the dividend multiplied by the fractional part of the quotient, the block can be replicated with the following code (a and b represent the inputs):
((a) - ((b) * ([floor v] of ((a) / (b)))))
If the result wanted is the remainder supposing the quotient is rounded towards 0, a Scratcher can either take the result of () Mod () block and subtract the dividend once, as so:
if <((a) / (b)) < > then set [r v] to (((a) mod (b)) - (b)) else set [r v] to ((a) mod (b)) end
or round the quotient towards 0 and compute the remainder from there:
set [q v] to ((a) / (b)) if <(q) > > then set [q v] to ([floor v] of (q)) else set [q v] to ([ceiling v] of (q)) end set [r v] to ((a) - ((b) * (q)))
- This is different from the remainder operator in most programming languages, which round negative quotients up, towards 0, but consistent with the "//" and "\\" messages in Smalltalk.