Wormbo: added related links to switch and conditional operator

2009-02-09T07:05:21Z

added related links to switch and conditional operator

Wormbo: New page: The '''if''' statement provides a simple way to branch code execution paths based on a condition. When the condition is met, a certain piece of code can be executed and optionally, when th...

2008-10-17T07:20:31Z

New page: The '''if''' statement provides a simple way to branch code execution paths based on a condition. When the condition is met, a certain piece of code can be executed and optionally, when th...

New page

The '''if''' statement provides a simple way to branch code execution paths based on a condition. When the condition is met, a certain piece of code can be executed and optionally, when the condition is not met, another piece of code can be executed.

==Syntax==
The simple '''if''' statement looks as follows:
'''if ('''''condition''''')'''
''statement''''';'''
The ''condition'' is a [[boolean]] expression and if it evaluates to ''True'' at runtime, the ''statement'' is executed.

If more than one code statement should be executed, simply enclose them all in curly braces:
'''if ('''''condition''''') {'''
...
'''}'''

Additionally, when the ''condition'' evaluates to ''False'', a different piece of code can be executed:
'''if ('''''condition''''')'''
''statement''''';'''
'''else'''
''statement''''';'''
Of course, this also works with a block of code:
'''if ('''''condition''''') {'''
...
'''} else {'''
...
'''}'''
You can even combine the block and simple forms:
'''if ('''''condition''''') {'''
...
'''}'''
'''else'''
''statement''''';'''
...or:
'''if ('''''condition''''')'''
''statement''''';
'''else {'''
...
'''}'''
To prevent confusion, it may be a good idea to always use curly braces, even if you only put a single statement after the '''if''' or '''else''' part.

=="ElseIf" statement==
The '''if''' statement in [[UnrealScript]] does not support an "elseif" clause, like e.g. BASIC dialects do. Instead, you can simply add another '''if''' clause in the '''else''' part:
'''if ('''''condition1''''') {'''
...
'''} else if ('''''condition2''''') {'''
...
'''} else if ('''''condition3''''') {'''
...
'''} else {'''
...
'''}'''

==The "dangling else" problem==
Consider the following example code:
<uscript>
if (a)
if (b)
doSomething();
else
doSomethingElse();
</uscript>
This looks highly ambigious. Which '''if''' does the '''else''' belong to? Indenting would suggest it belongs to the first '''if''' statement. However, the compiler ignores all indenting, so the '''else''' may as well belong to the second '''if''' statement.

Using curly braces, the above code may look as follows:
<uscript>
if (a) {
if (b) {
doSomething();
}
} else {
doSomethngElse();
}
</uscript>
Or like this:
<uscript>
if (a) {
if (b) {
doSomething();
} else {
doSomethngElse();
}
}
</uscript>
Obviously these two implementations are not the same, but which one would be used if you left out the curly braces?

This problem is called "dangling else" and the compiler solves it by applying a simple rule: ''An else statement always belongs to the inner-most preceeding if statement.'' In our case, this is the "if (b) statement".

{{navbox unrealscript}}

@@ Line 67: / Line 67: @@
+   }
 } else {
-   doSomethngElse();
+   doSomethingElse();
+}
 </uscript>
@@ Line 76: / Line 76: @@
      doSomething();
    } else {
-     doSomethngElse();
+     doSomethingElse();
+   }
+}
@@ Line 84: / Line 84: @@
 This problem is called "dangling else" and the compiler solves it by applying a simple rule: ''An else statement always belongs to the inner-most preceeding if statement.'' In our case, this is the "if (b) statement".
 {{navbox unrealscript}}

If statement - Revision history

Wormbo: added related links to switch and conditional operator

Wormbo: New page: The '''if''' statement provides a simple way to branch code execution paths based on a condition. When the condition is met, a certain piece of code can be executed and optionally, when th...