What is this technique called?

[ShakeyPakey]

Hello, everyone, I have a small question.

I'm new to BASIC overall and decided to pick it up. While looking through a program coded in it so I can learn, I saw that they used a technique of skipping to parts of code they want to run by typing "GOTO {line number}", or just saying "IF {expression} then GOTO {line number}" at least I believe it's a line number. The author put a number at the start of every line that goes up by 10 each line, and sometimes it goes up by hundreds. This is a snippet:

Code: Select all

10 PRINT "Hello. How old are you?"
20 INPUT A
30 IF A < 13 THEN 100
40 PRINT "You're older than 13."
50 END 
100 "You're younger than 13.
110 END

Can someone tell me what this method is called (if anything) and how it can be useful?

Thank you :)

[Imortis]

That code is quite old. FreeBASIC still supports line numbers but there are much better and easier ways to do the thing you are describing.

Code: Select all

PRINT "Hello. How old are you?"
INPUT A
IF A < 13 THEN 
	print "You're younger than 13."
ELSE
	PRINT "You're older than 13."
END IF

[Lost Zergling]

http://ingeb.org/songs/vemkanse.html
https://www.youtube.com/watch?v=Hl76XbZp3js
This technique is called "the sailing navy" (the beginnings)

[ShakeyPakey]

That code is quite old. FreeBASIC still supports line numbers but there are much better and easier ways to do the thing you are describing.

Code: Select all

PRINT "Hello. How old are you?"
INPUT A
IF A < 13 THEN 
	print "You're younger than 13."
ELSE
	PRINT "You're older than 13."
END IF

Yes, I am aware that it is quite old & inefficient (this was found in a program written in 1978), and I know of the more efficient way you've stated. I'm just curious that if they're considered labels or line numbers?

[Imortis]

Technically labels and line numbers are the same thing in FB. So yes, you could say they are labels.

[dodicat]

Coding this way is generally called branching.
https://en.wikipedia.org/wiki/Branch_(computer_science)

[caseih]

And all languages on all computer architectures ultimately translate to this form form of logic. This is known as being "turing complete." In fact you can write any program you want with only one instruction that involves an arithmetic operation and a branch (goto) based on a test of the result of the arithmetic operation.

A common idiom when programming in assembly language (a step above pure machine language) is to take your IF/THEN block and then invert the condition. So you get something like:

Code: Select all

if a = 5 then
    'do something
end if

which translates to something like

Code: Select all

if a != 5 then goto label1
'do something'
label1:

GOTO may be considered bad form today with modern, structured constructs, but everything ultimately compiles down to a bunch of gotos! Technically conditional branches.