added structkeyexits and looping through structure sections

cfml100mins.markdown

@@ -12,6 +12,8 @@ ColdFusion Markup Language (CFML) is a web programming language, which is especi
     2. Looping Through Results
 7.  [Arrays](#arrays)
 8.  [Structures](#structures)
+    1. structKeyExists Function
+    2.  [Looping](#structureLooping)
 9.  [Conditionals](#conditionals)
     1.  [If, Else If, & Else](#if)
     2.  [Looping](#loop)
@@ -1050,6 +1052,53 @@ The last chunk of the example used ```StructSort``` to get the sorted array "stu
 
 While that last part probably seemed complicated, it's just to illustrate that structures are unordered.
 
+<a name="structKeyExists">
+### 8.3 structKeyExists
+</a>
+When referencing a structure by key names, it is ususally good practice to make sure that the key exists in the structure first. This is done with the ```cfm structKeyExists(structure, key) ``` function.  Lets say we have a structure named Person and we want to check that it has a key named "yearBorn" before doing something with it.  That would be done with the following code:
+
+```cfm
+<cfscript>
+if(structKeyExists(Person,"yearBorn")){
+  Person.age = year(now()) - Person.yearBorn;
+}
+</cfscript>
+```
+
+<a name="structureLooping">
+### 8.2 Looping through a structure
+</a>
+
+Sometimes it is convienent to loop through all the keys of a structure.  This is done with a for-in type of loop.  Lets look at an example using the following struct:
+
+```cfm
+<cfscript >
+  myStruct = {apple = "Apple", banana = "Banana", pear = "Pear"};
+</cfscript>
+```
+
+#### Tag Syntax
+
+Using tag syntax we use what is called a "collection" loop.  The cfloop syntax takes two parameters, the name of the collection, and the variable name that holds the collection's key:
+
+```cfm
+<cfloop collection="#myStruct#" item="fruit">
+  #myStruct[fruit]#
+</cfloop>
+```
+
+#### Script Syntax
+
+Using script syntax we use what is called a "for-in" loop.  The syntax of a for-in loop looks like ```cfm for(key in structure)```.  The code to loop through the structure we created earler would look like this:
+
+```cfm
+<cfscript >
+  for(fruit in myStruct){
+    writeOutput(myStruct[fruit]);
+  }
+</cfscript>
+```
+
 <a name="conditionals" >
 ## 9. Conditionals
 </a>