Difference between revisions of "Control Structures"

Revision as of 08:27, 22 August 2005

if

The if construct is one of the most important feature of many languages, the EasyUO scripting language included. It allows for conditional execution of code fragments. The basic syntax of the command is:

if ( expression )
	statement

As described in the section about expressions expr is evaluated to its boolean value. If it evaluates to #true the statement will be executed.

The following code fragment will display 'a is bigger than b' if %a is bigger than %b:

initEvents

set %a 1
set %b 0
if %a > %b
	event SysMessage a is bigger than b

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 statement group. For example, this code would display a is bigger than b if %a is bigger than %b, and would then assign the value of %a into %b:

initEvents

set %a 10
set %b 2
if %a > %b
{
	event SysMessage a is bigger than b
	set %b %a
}

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.

else

Often you would want to execute a statement if a certain condition is met, and a different statement if the condition is not met. This is what else is for. else extends an if statement to execute a statement in case the expression in the if statement evaluates to #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:

initEvents

set %a 10
set %b 20
if %a > %b
{
  event SysMessage a is bigger than b
}
else
{
  event SysMessage a is NOT bigger than b 

Note:
Right now it is not possible to nest if commands and use else. Only one if, if you are using else.

for The for loop is a loop that counts a variable either up or down.

for variable from_value to_value
{
	statement
}

The loop starts by assigning the from_value to the variable, runs the loop. Then it either increments or decrements, depening on which way the loop is going, running the loop for each value.

Note
At the moment, you must ALWAYS use brackets with FOR. 

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.

Note
Don't GOTO out of a sub. Always use return! EasyUO will probably not crash but it is VERY bad programming style. 

Currently, inline comments don't work with the sub command (this'll get fixed in a future update).

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

goto The goto command moves the execution to another part of the script. The destination point is given by a label.

goto label_name 

Labels A label specifies a point in the code where you can goto to.

label_name:

User Contributed Notes

'''/docs/control-structures.php'''