I am having requirment like 
I am using Pageblocktable in which i have some data and in one column i have given the link called view after clicking on view that particular detail should be viewd..
But it is not working correctly..
I am sharing my code with you

Visualforce

<apex:PageBlockSection columns="1" >
     <apex:pageBlockTable value="{!getc}" var="a">
         <apex:column value="{!a.Name}"/>
         <apex:column value="{!a.customer__c}"/>
         <apex:column value="{!a.E_mail__c}"/>
         <apex:column value="{!a.Phone_Number__c}"/>
         <apex:column headerValue="Action">
         <apex:commandLink value="view" reRender="imagepopup" action="{!addcomp}">
             <apex:param id="custid" value="{!a.id}"/>
         </apex:commandLink>
         </apex:column>
     </apex:pageBlockTable>
 </apex:PageBlockSection>

apex code

public Complaint__c add{get;set;}

public List<Shan__Complaint__c> getc{get;set;}

  public refreshctrl ()
    {
         
        
         getc= [Select id,Name,Shan__customer__c,Shan__E_mail__c,Shan__Phone_Number__c,Shan__Issue_Details__c,Shan__Issue_Summary__c from Shan__Complaint__c]; 
          
    }

public void addcomp()
    {
        ID fid=ApexPages.currentpage().getparameters().get('custid');
        add=[Select id,name,customer__c,E_mail__c,Phone_Number__c,Issue_Summary__c,Issue_Details__c from Complaint__c where id=:fid];
        displayPopUp=true;
       // return new Pagereference('/apex/viewcomp?id='+lid);
        
        
    
    }

It is giving me error:
Visualforce ErrorHelp for this Page
System.QueryException: List has no rows for assignment to SObject
Error is in expression '{!addcomp}' in page shan:cust_complaint: Class.Shan.refreshctrl.addcomp: line 37, column 1
Class.Shan.refreshctrl.addcomp: line 37, column 1