try this in cotroller.
for (counter in 0..reportCount - 1) {
String report = params["reportName${counter}"]
println "==${counter}===${report}====="
}
also you should use your each loop on gsp page like this..
<g:each in="${allReports.toList()}" var="each" status="i" >
<g:hiddenField name="reportName${i}" value="${each}" />
</g:each>
Enjoy.