More complicated if statement - ComputerCraft Forums (archive)

Crowdy199 #1

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34 posts

Posted 15 January 2013 - 11:20 AM

I am making and os where and there is a tool bar at the bottom i am using the mouse in the os now i no how to do that by using if x == whatever number and y == whatevet number so what i dony get is how to do this i want them to be able to do whatever they want unless they click whatever spot then run this code so plz tell me how to do that thank u

theoriginalbit #2

7508 posts

Location Australia

Posted 15 January 2013 - 11:37 AM

This is what I posted in a topic yesterday… :)/>

Conditionals are definitely a very important part of programming that everyone needs to know… that being said here goes…

Explaination of if's and boolean logic:

Spoiler

If statements
An if statement is a way of performing particular instructions given a certain condition… these conditions can be a single boolean (true/false) variable or a set of statements that produce a boolean… basic Lua syntax of an if statement is:


if <condition> then
  -- instructions to perform when condition is true
end

Boolean Logic
An if statement's conditional can then be furthered using boolean logic ( not, and, or ) using not, and, or all can effect the condition.
code example


if ( active and running ) or not waiting then
end

where active, running and waiting are all boolean variables

A not effects in this way


not true = false
not false = true

An and effects in this way


true and true = true
true and false = false
false and true = false
false and false = false

An or effects in this way


true or true = true
true or false = true
false or true  = true
false or false = false

As shown in the coding example you can also use brackets to make sure that those statements are evaluated first. For examples using


if not ( running and listening ) then

would only do the actions if running AND listening are false

Ifelse statements

Ifelse statements work in the exact same way as with the if statements except they provide one advantage, if we wished to do something based on a condition, without ifelse we would do this


if <condition> then
  -- what to do when condition is true
end

if not <condition> then
  -- what to do when condition is not true
end

however with ifelse statements we can do the following



if <condition> then
  -- what to do when condition is true
else
  -- what to do when condition is false
end

now ifelse statements can also be extended when dealing with variable equality as follows


if input == "this" then

elseif input == "that" then

elseif input == "the other" then

end

we can also end the above code with an aditional else, just incase it doesn't match anything


if input == "this" then

elseif input == "that" then

elseif input == "the other" then

else

end

Nested ifs
We can also have if and ifelse statements inside another if or ifelse statement. the basic syntax is as follows


if <first condition> then
  if <second condition> then
  else
  end
end

This code will only reach the second condition IF the first condition is true…

Pro tip:

Spoiler

Lets say that we want to assign a variable x to 10 if a boolean is true or 20 if it is false, normally people would use an if statement as follows


local x
if someBoolean then
  x = 10
else
  x = 20
end

However we can use a (what is referred to in other languages) ternary operator…
A ternary operator works in this way


<condition> and <value if true> or <value if false>

so for the example above we would do the following


x = running and 10 or 20

now lets say we want to assign to the variable x the value 20 ONLY if the variable y has no value (is nil) we can do the following


x = y or 20

we can also assign a boolean variable like so


var = <value 1>  and <value 2>

This will only assign true to var if BOTH value 1 and value 2 are not false or nil

We can also use


var = <value 1>  or <value 2>

This will assign true to var if either value 1 or value 2 is not false or nil
Obviously this can be extended into any combination not, and, or and brackets to gain order… but beware, the longer it is the more complicated it gets


var = not ( <value 1> and <value 2> or <value 3> ) and <value 4> or not <value 5>

Off the top of my head I think I have covered everything, I hope I'm not forgetting anything and that it all makes sense, it made sense in my head ;)/>

Edited on 15 January 2013 - 10:47 AM

sonmica #3

sonmica's profile picture

1 posts

Posted 15 January 2013 - 06:02 PM

Crowdy199, on 15 January 2013 - 11:20 AM said:
I am making and os where and there is a tool bar at the bottom i am using the mouse in the os now i no how to do that by using if x == whatever number and y == whatevet number so what i dony get is how to do this i want them to be able to do whatever they want unless they click whatever spot then run this code so plz tell me how to do that thank u

You will need to define a rectangle for where you want your toolbar to be in, and then when there is a mouse click event, it runs a check to see if the mouse has been clicked inside the rectangle.

Define your rectangle with boundaries, say:
toolbar_left – x coordinate
toolbar_right – x coordinate
toolbar_top – y coordinate
toolbar_bottom – y coordinate

Your conditional checks whenever you receive a mouse click event would be this (assuming x=0 is at the left of the screen and y=0 is at the top of the screen):


if ( mouseclick_x > toolbar_left ) and ( mouseclick_x < toolbar_right ) and ( mouseclick_y > toolbar_top ) and ( mouseclick_y < toolbar_bottom ) then
-- toolbar is clicked, do toolbar stuff
end

hope this helps.

ChunLing #4

ChunLing's profile picture

2005 posts

Posted 15 January 2013 - 06:43 PM

The real problem is making it so that the user "able to do whatever they want unless they click". This involves either having an os.pullEvent() loop that handles all other kinds of events as well as mouse clicks or making use of the parallel api functions.