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() Mod ()
() mod ()
Category Operator
Type Reporter

The () Mod () block ("mod" is short for "modulo") is an Operators block and a reporter block. The block 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]

Example Uses

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)) = [0]> 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)) = [0]> 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)) = [0]> then
    say [a is an even number]
else
    if <((a) mod (1)) = [0]> 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 [0]
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

Workaround

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)) < [0]> 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) > [0]> 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)))

See Also

Notes

  1. 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.