global class CallingFromTrigger implements DataBase.Batchable<sObject>{
    List<Contact>contlist=new List<Contact>();
    global CallingFromTrigger(List<Contact>clist){
        contlist=clist;   
    }
    global DataBase.QueryLocator start(Database.BatchableContext BC){
        return(DataBase.getQueryLocator([SELECT Id,Email FROM Contact WHERE Id IN:contlist]));
        
    }
    global void execute(Database.BatchableContext BC,List<Contact>Scope){
        for(Contact c:Scope){
            c.Description='if Email available then we have sent email';
            
        }
        Database.update(Scope);
    }
    global void finish(Database.BatchableContext BC){
        for(Contact c:contlist){
            if(c.Email!=null){
                Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
                mail.setToAddresses(new String[] {c.Email});
                mail.setSubject('Added in Contact');
                String messageBody = 'Hii you are added in contact';
                mail.setPlainTextBody(messageBody);
                Messaging.sendEmail(new Messaging.SingleEmailMessage[] {mail});
            }
        }
    }
    
}