Syntax to learn today: If loop ; Break[];

amount=1000;interestrate=0.02;installment=100;

Do[interest=amount*interestrate;
amount=amount+interest - installment;
(* comment *)
(*
Print["This is the ",n," week.The amount I owe a long is ",amount];*)
If[amount<0,
Print["In the ", n," week, amount becomes negative"];
Break[];
];(*end if *)

,{n,1,20,1}];