Difference Between Style variable & Render Variable

Render Variable: - Specify a variable based on which object can be conditionally rendered. 

Style Variable: - Specify a variable based on which object can be conditionally styled. Style variable is               used to show or represent different report objects in different styles that are present in report.

Example  for Style Variable

In a report in a list if u want to display every alternate row with particular color 
in this case, go to query explorer....
1) create a data item with name running-count with function "running-count" on particular unique column
2) now create one more data item as mod  with functon "mod" on that running-count data item.

    Select List and in properties pane..select 'Properties' and select 'running-count' and 'mod' data items.
3)create a boolean varibale with expression mod=1
4)go to the page select List column Body style
5)In properties pane select Style Variable as boolean variable 
6)click on YES variable and set its Foreground color as RED 
7)click on No variable and set its Foreground color as Yellow 
now run the report 



Example  for Render Variable

if the case is like you want to see the  particular page in HTML or PDF or CSV format then 
1)Create 3 pages in your report 
2)every page conatins some specific data
3)name these pages as HTML,PDF,CSV
4)create a String vaiable with 3 values as HTML ,PDF and CSV
5)now in string variable put expression as .....
case

when ReportOutput()='HTML' then 'HTML'
when ReportOutput()='PDF' then 'PDF'
when ReportOutput()='CSV' then 'CSV'
end 

6)now go the page named HTML and select page object 
7)in properties pane click on Render Variable ,select that string variable
8)check only HTML check box value for HTML page 
9)repeat step No. 6 to step No.8 for remaining 2 pages.