Lua - Conditionals and loops

Lua module U103

Conditionals and loops

Exercises, examples and other material relating to training module U103. This topic is presented on public courses Learning to program in Lua, Lua Programming, Lua Programming

Articles and tips on this subject		updated
4574	repeat until in Lua - a one or more rather than a zero or more loop The "repeat until" structure in Lua provides a loop with condition checking at the end - in other words, it's a "one or more times" loop, unlike while which is a "zero or more times" loop. Syntax - straightforward; example: repeat io.write("How many people? ") said ...	2015-11-05 (short)
4323	Learning to program - Loop statements such as while If your program always ran each statement just once (indeed skipping over statements which were in blocks in false conditions) it would run very quickly and would have little use. You couldn't (for example) run a program which went through a whole series of results from a database query and displayed ...	2014-11-22
4322	Learning to Program - the conditional statement (if) Every language has some sort of conditional statement. That's a way of looking at some sort of setting or status in the program and performing some sort of action based on that setting or status. such statements take the form ... if {some sort of condition is true} then {run a group of ...	2014-11-22 (longer)
4272	Lazy operators in Lua - what they mean, and examples If you use the word or in an expression in Lua, the expression to the right of the word will only be evaluated and returned of the value to the left is nil. So a very common idiom is: stuff = stuff or {} which means "if stuff already has a value, leave it alone - otherwise make it an empty ...	2014-05-06
3397	Does a for loop evaluate its end condition once, or on every iteration? All the languages that we teach have a for loop or the equivalent, which is a clean way of repeating a block of code with a rising or falling index number. It's used in many circumstances - for example in iterating through the months of the year (for m goes from 1 to 12) of in stepping through all ...	2012-04-15
3686	The goto statement in Lua In the past there was considerable debate in academia and industry on the merits of the use of goto statements, and indeed Lua didn't have them until release 5.2. Well used in Lua, they can provide an escape from inner loops, jumping to a label using a ::label:: format. For example: for ...	2012-04-07
3558	Python or Lua - which should I use / learn? "Should I learn and use Python or Lua" - a question to me. The questioner was perceptive, knowing that he shouldn't try to learn lots of languages at the same time, and that he should always limit the "basket" of languages used within his applications - in fact, he was wondering if he could select just ...	2011-12-24 (longer)
2454	For loops in Lua As an old Fortran programmer, I remember that a for loop was given a start point, an end point and a step ... and they had to be whole numbers (integers). Lua's for loops can be used that way, but they can be used a lot more flexibly too. From, to, step for loops Th egood news is that Lua works in ...	2009-10-17
2455	Lua examples - coroutines, error handling, objects, etc I have presented a bespoke Lua course over the last three days ... and it has lead me to some interesting new examples which I'm sharing here. Object Orientation is more a way of thinking and coding than a language feature in Lua - when you set up a piece of data / structure / object, you do so in a ...	2009-10-17
2351	Ternary operators alternatives - Perl and Lua lazy operators "If the gender is male, the answer is him, but if the gender is female, the answer is her". A common situation in programming - [is/are], [him/her], [yes/no], [child/children], [ice/water/steam], [public/private] - and C and Perl and PHP provide the "ternary" operator ? and : to provide a shorthand ...	2009-08-12
1738	Clean code, jump free (Example in Lua) The "goto" statement - in languages that still support it - is regarded with disdain by Computer Scientists as it makes for spaghetti code - hard to follow and going all over the place! In some ways, loop controls "break" and "continue" ("last", "next" and "redo" in Perl; "next", "redo", "retry" and ...	2008-08-07
1696	Saying NOT in Perl, PHP, Python, Lua ... "Isn't there one standard way to say NOT?" asked one of my delegates on today's course - and it's an excellent question. But the answer to a question about a negative subject is itself in the negative - no, there isn't just a single way! In fact .. I can think of no fewer that 12 ways! • 1. ! ...	2008-07-05
1685	Short circuit evaluation (lazy operator) in Lua In Lua, if a partial expression evaluates to true the following section will NOT be evaluated if it follows an or because the whole thing cannot be true. If a partial expression evaluates to false, the following section will NOT be evaluated if it follow an and because the whole thing must be true. If ...	2008-06-23

Examples from our training material

andor	Lazy and / or operators
bpm	string.find v string.gfind
clike	for loop with pairs and ipairs
clumpit	for loop termination
doco	Changing loop counts
exa	Loops and conditionals - exchange rate example
floo	for loop in which end condition changes
kz	Example of a for loop
lif	if, elseif, else
ll2	while loop and repeat until loop
lloops	while and for loops
lsx	Lua for loop - termination
meerkat	Lazy Operators
runt	repeat until
swans.lua	Swan family - Lua
tchart	for loop with start, end and step
wcd	Comparison of while and until loops
whilly	Writing cleaner code without break or continue

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from [here].

Topics covered in this module

If while repeat break do and for.
Comparing numbers comparing strings.
Equality and nil.
Combining Conditions.

Complete learning

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