Arithmetic

Add, subtract, multiply, divide — and what to do when there are two operations

easyYou need: How the processor works

The op block has four fields: where to put the answer, what to do, and the two numbers it is done to. Numbers can be written straight into the fields or supplied as variables — the block does not care.

steptick 0

Set0

=

Set1

=

Operation2

=

+

Operation3

=

-

Operation4

=

*

Operation5

=

/

@counter0number

anullnull

bnullnull

sumnullnull

differencenullnull

productnullnull

quotientnullnull

The first two lines put numbers into a and b, the other four compute. The variables window shows all four answers at once:

Operation	In the block	What it computes	Answer with a = 12, b = 5
add	+	addition	17
sub	-	subtraction	7
mul	*	multiplication	60
div	/	division	2.4

Division is ordinary, not integer: 12 divided by 5 is 2.4, and the fractional part does not go anywhere. How to get a whole number and a remainder is in the lesson «Whole numbers and precision».

One operation per line

The familiar total = (a + b) * 2 does not exist in mlog. The instruction does exactly one thing, so an expression unfolds into a chain, with the intermediate answer put into a variable:

steptick 0

Set0

=

Set1

=

Operation2

=

+

Operation3

=

*

@counter0number

anullnull

bnullnull

sumnullnull

totalnullnull

First sum becomes 17, then that same value goes into the multiplication — and total comes out as 34. The name sum is not special here but invented: an intermediate answer can be called anything.

Note

The order of operations is set by you, through the order of the lines. There is no “multiplication before addition” in mlog, because there is no expression inside which that order would be needed.

Operations that need no second number

Half the operations need no second argument at all, and the editor simply does not show it: choose abs and the second field disappears. That is how absolute value, square root, rounding and trigonometry work.

op abs answer -5 gives 5, op sqrt answer 81 gives nine. One field is left, because one number is all the work needs.

Three more useful ones

Operation	In the block	What it does	Example
pow	^	raises to a power	op pow answer 2 10 → 1024
max	max	takes the larger of two	op max answer 3 7 → 7
min	min	takes the smaller	op min answer 3 7 → 3

max and min are the usual way to keep a number inside bounds: max with the lower one first, then min with the upper, and the value is clamped between them.

Remember

• op has four fields: where, what to do, and two numbers.
• Numbers can be written into the fields or supplied as variables.
• One operation per line; a complex expression is several lines and an intermediate variable.
• div divides evenly only by accident: 12 / 5 is 2.4.

Task

Change b in the example from 5 to 0 and look at quotient.

The variable holds null. Division by zero gives infinity, and infinity is not stored in mlog at all: the variable becomes the object null instead. The program does not crash and does not stop — it carries on with null instead of a number, and in the very next piece of arithmetic that counts as zero. Checking the divisor before dividing is your job, not the processor’s.