Often when designing a Reporting Services with parameters you may be required to display those parameter values on your report. This is beneficial when you have a lot of values for one parameter or maybe you just want to print the report and need to know how the report is being filtered.
Normally if you would like to use a parameter anywhere in the design of your report you can simply drag in the parameter name from the Report Data tab. Here I’ve concatenated the parameter value with some text:
="Category: "+Parameters!Cat.Value
However, when you have a parameter that can have multiple values you will run into an issue with displaying these parameter values correctly.
The problem it is displaying an array where normally a single value would be placed. The fix for this is a pretty simple function that exists in Reporting Services called Join. By changing my parameter textbox to the following:
=”Category: “+Join(Parameters!Cat.Value, “, “)
Making changes places the array in a comma delimited list visible to the user.
Devin Knight 
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