Can't use the Same Name in the Same Scope

It is a mistake to use the same identifier twice in the same scope. For example, the following is a mistake:

class CheckingAccount
{
  . . . .
  private int    balance;

  void processCheck( int  amount  )
  {                          
    int amount;    

    incrementUse();
    if ( balance < 100000 )
      charge = 15; 
    else
      charge = 0;

    balance =  balance -  amount  - amount  ;
  } 

}

The scope of the formal parameter (amount) overlaps the scope of the local variable ( also named amount), so this is a mistake. This is a different situation than the previous one where two separate formal parameters were both named amount. In that situation the scopes did not overlap and there was no confusion.