trigger UpdateProjectNo on Project__c (before update) {
//Look for project status update. Check if its associated to junction object
//Update no of projects field in Account object
for (Project__c p : Trigger.new) {
    if (p.status__c != Trigger.oldMap.get(p.id).status__c) {
    if (p.Status__c == 'Active') {
        //List related records from junction object
        List<Account_or_Project__c> junctionId = [select id,Account_Name__c
                                                 from Account_or_Project__c
                                                 where Project_Name__c  = :p.id];
        if (junctionId.size() > 0) {
            //Loop through the list of records
            for (integer i = 0; i < junctionId.size(); i++) {
            //Get related Accounts
            List<Account> acc = [select id,No_Of_Projects__c from Account
                                where id = :junctionId.get(i).Account_Name__c];
            for (Account myAcc : acc) {
                myAcc.No_Of_Projects__c++;
                update myAcc;
              }
           }
         }
       }
    }
  }
}