Choosing a value without a branch

A branch for the sake of one value is unnecessary — but select is not always needed either: a comparison already has an answer

easyYou need: Condition and branching, Comparisons and logic

select puts one of two values into a variable: the first if the condition holds, the second if it does not. In the block it reads as words: total = if copper >= 100 then 1 else 0.

Before picking it up it is worth understanding when it is not needed — otherwise people start writing with it what is shorter without it.

steptick 0

Sensor0

=

 in

Operation1

=

>=

Select2

= if

>=

then else

Select3

= if

<

then else

@counter0number

coppernullnull

enoughnullnull

captionnullnull

howManynullnull

Press “step” four times.

When select is not needed

The example’s second line is op greaterThanEq enough copper 100, and enough ends up holding a one. No choice was required: a comparison answers with a one or a zero by itself, and that is already a finished value.

Silent failure

So select enough >= copper 100 1 0 is wasted work: the same one and zero come out of a single op. If both of your values are 1 and 0, what you need is not select but a comparison. More on that in the lesson «Comparisons and logic».

When it is the right tool

As soon as the values stop being one and zero, a comparison stops helping.

The third line chooses between two strings: caption becomes “enough”. That cannot be had through op at all — a comparison can only answer with a number.

The fourth line — select howMany lessThan copper 100 copper 100 — caps a number from above: if there is less than a hundred copper, take what there is; otherwise take exactly a hundred. howMany ends up as 100.

The general rule: select is needed when both values are arbitrary — numbers other than zero and one, strings, items, buildings, variables.

What is being chosen	With what
a one or a zero by a condition	op with a comparison
one of two ready values	select
one of two actions	jump: that is a branch, not a value
the larger or smaller of two numbers	op max and op min — shorter

It chooses a value, not an action

Both halves of select are values that already exist: numbers, strings, variables, objects. The instruction runs nothing and skips nothing, it simply takes one of two.

Silent failure

Calculations cannot be hidden in the fields: total = if … then a+1 else a-1 cannot be written, because a+1 is an operation, not a value. You compute in advance, in two op lines, and select takes what is already computed.

And both halves are computed — including the one that will not be taken. If the calculation is expensive, jump is cheaper: it does skip what is not needed.

The conditions are the same as jump’s

There are eight of them, and the buttons carry the same signs — ==, ===, not and the rest from the table. The words “if”, “then” and “else” in the block are a translation; without it they are if, then, else.

Remember

• select puts one of two ready values into a variable by a condition.
• If the values are one and zero, select is not needed: the comparison itself gives the answer.
• Only it can choose between strings, items and arbitrary numbers.
• An action is chosen by branching, not by select.
• The conditions and their labels are the same as jump’s.

Task

Change the condition in the third line to lessThan and run the example again: caption becomes “low”, although there is still 120 copper. The values stayed where they were — the first is still the one for “true”, it is just that “true” now means something else.

Then type copper instead of 100 in the second half of the fourth line: the cap disappears, and howMany equals the copper whatever the condition. That shows both halves are ordinary values, and nothing stops you putting the same thing in both.