Difference between revisions of "Control Structures"

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==if==
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[[Category: Language Reference]]
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__TOC__
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==Goto's==
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Goto's are an archaic and powerful command to automatically move to a different point in a program. They never [[return]] unless another goto is used. They should <b>never</b> be used to return from a subroutine.
  
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The “if” construct, one of the most important features of many languages including EasyUO, allows for conditional execution of code fragments. The basic syntax of the command is:
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===label===
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A [[label]] is a marker for the point a goto command will jump to. These are created by using any word that isn't a command, and suffixing it with a colon, like this...
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<pre>mylabel:</pre>
  
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If ( expression )
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===goto===
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A [[goto]] is used to jump directly to a label as defined above. This is accomplished by using [[goto]] {label}
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<pre>goto mylabel</pre>
  
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{ statement }
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{{note|You must never use goto to jump out of a sub! Use return to properly terminate a sub routine. To prevent a stack overflow, EUO only supports 1000 consecutive GoSubs without returning. Remember this when using recursion! When the GoSub stack is about to get 1001 levels, the very first level in the bottom of the stack is deleted to make room.}}
  
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As described in the section about [[Expressions]], expression is evaluated as a Boolean value. If it evaluates to [[var_true|#true]] the statement will be executed.
 
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The following code fragment will display a message box with the phrase "a is greater than b" ''if'' the value in the variable %a is greater than the value in the variable %b:
 
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<pre>
 
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set %a 1
 
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set %b 0
 
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if %a > %b
 
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display ok a is greater than b
 
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halt</pre>
 
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Often you would want to have more than one statement executed conditionally. Of course, there is no need to wrap each statement in an “if” clause. Instead, you can group several statements into a code block by using braces. For example, this code would display a message box with the phrase "a is greater than b" ''if'' the vaule in the variable %a is greater than the value in the variable %b, and would then assign the value of %a into the variable %b:
 
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<pre>
 
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set %a 10
 
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set %b 2
 
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if %a > %b
 
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{
 
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display ok a is greater than b
 
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set %b %a
 
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}
 
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halt</pre>
 
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“if” statements can be nested indefinitely within other “if” statements, which provides you with complete flexibility for conditional execution of the various parts of your script.
 
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==else==
 
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Often you would want to execute a statement or code block if a certain condition is met, and a different statement or code block if the condition is not met. This is the purpose of the else statement. Else extends an “if” statement to execute a statement or code block only in the instance that the expression of the previous if statement evaluates to [[var_false|#false]]. For example, the following code would display a is bigger than b if %a is bigger than %b, and a is NOT bigger than b otherwise:
 
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<pre>
 
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set %a 10
 
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set %b 20
 
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if %a > %b
 
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{
 
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display ok a is greater than b
 
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}
 
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else
 
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{
 
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display ok a is less than b
 
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}
 
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halt</pre>
 
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{{Note|In EasyUO 1.4 it is not possible to nest if commands and use else. The method around this limitation is to use an additional if to test for the opposite condition. In EasyUO 1.5, if and else can be safely nested however.}}
 
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==for==
 
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The “for” loop is a loop that iterates a variable either up or down upon execution of the code block that it controls. The code block is executed with each iteration until the second value is reached.
 
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<pre>
 
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for variable from_value to_value
 
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{
 
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statement
 
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}</pre>
 
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The loop starts by assigning the ''from_value'' to the variable, runs the statement(s) inside the code block. The variable is then incremented or decremented as required for the variable to be one integer value closer to the ''to_value''. The statement inside the code block is executed after each and every iteration of the variable.
 
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''Note: in EasyUO 1.4, brackets are required to be used with a for statement, even if the code block consists only of a single statement. As of EasyUO 1.5, if the code to be executed with a for statement is only a single statement, the braces are optional.''
 
  
 
==Subs==
 
==Subs==
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The term sub is short for subroutine. Subs are an important feature of the EasyUO script, that will make your scripts more logically structured, easier to read, and will make you have to write less code.
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The term <i>sub</i> is short for subroutine. Subs are an important feature of the EasyUO script that will make your scripts more logically structured, easier to read, and will make you have to write less code.
  
 
A basic sub definition starts with a sub statement followed by the subs name (sub names are case insensitive), a number of script lines and ends with a return statement.
 
A basic sub definition starts with a sub statement followed by the subs name (sub names are case insensitive), a number of script lines and ends with a return statement.
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If parameters were added to the calling gosub command they will be present in the variables %1, %2, and so on. The variable %0 holds the number of parameters passed. As all variables are in the global scope, the %0, %1, %2.. will be overwritten if you call another sub from inside a sub.
 
If parameters were added to the calling gosub command they will be present in the variables %1, %2, and so on. The variable %0 holds the number of parameters passed. As all variables are in the global scope, the %0, %1, %2.. will be overwritten if you call another sub from inside a sub.
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''Warning: Do not GOTO out of a sub, always use return! EasyUO will probably not crash but it is '''very''' bad programming style.''
 
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''Note: inline comments do not work with the sub command in EasyUO 1.4.
 
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This has been fixed in EasyUO 1.5 however.''
 
  
 
===gosub===
 
===gosub===
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<pre>
 
<pre>
 
return</pre>
 
return</pre>
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==goto==
 
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The '''goto''' command moves the execution to another part of the script. The destination point is given by a label.
 
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<pre>
 
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goto label_name </pre>
 
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===Labels===
 
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A label specifies a point in the code where you can '''goto''' to.
 
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<pre>
 
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label_name:</pre>
 

Latest revision as of 11:17, 3 August 2007

Goto's

Goto's are an archaic and powerful command to automatically move to a different point in a program. They never return unless another goto is used. They should never be used to return from a subroutine.

label

A label is a marker for the point a goto command will jump to. These are created by using any word that isn't a command, and suffixing it with a colon, like this... 

mylabel:

goto

A goto is used to jump directly to a label as defined above. This is accomplished by using goto {label} 

goto mylabel
Note: You must never use goto to jump out of a sub! Use return to properly terminate a sub routine. To prevent a stack overflow, EUO only supports 1000 consecutive GoSubs without returning. Remember this when using recursion! When the GoSub stack is about to get 1001 levels, the very first level in the bottom of the stack is deleted to make room.


Subs

The term sub is short for subroutine. Subs are an important feature of the EasyUO script that will make your scripts more logically structured, easier to read, and will make you have to write less code.

A basic sub definition starts with a sub statement followed by the subs name (sub names are case insensitive), a number of script lines and ends with a return statement. 

sub testSub
  ...
  return

If parameters were added to the calling gosub command they will be present in the variables %1, %2, and so on. The variable %0 holds the number of parameters passed. As all variables are in the global scope, the %0, %1, %2.. will be overwritten if you call another sub from inside a sub.

gosub

The gosub command transfers the execution to a sub with the name given by the parameter. 

gosub sub_name

Parameters can be added after the sub name. They will be transfered in the variables %1, %2, and so on. The variable %0 holds the number of parameters passed.

return

The return command transfers the execution back to where the sub was called using gosub. 

return
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