100 CLS: PRINT@6,"MORTGAGE CALCULATOR"
110 PRINT@64,"SELECT ONE OF THE FOLLOWING:"
120 PRINT@96,"1. GIVEN MONTHLY PAYMENT,"
130 PRINT@131,"INTEREST RATE, AND YEARS,"
140 PRINT@163,"FIND PRINCIPAL"
150 PRINT@224,"2. GIVEN PRINCIPAL, INTEREST,"
160 PRINT@259,"AND YEARS, FIND MONTHLY"
170 PRINT@291,"PAYMENT"
180 PRINT@352,"WHICH ONE";: INPUT A$
190 IF A$="1" THEN 210
200 IF A$="2" THEN 350
210 PRINT@448,"INVALID SELECTION--TRY AGAIN"
220 FOR T=1 TO 300: NEXT T: GOTO100
230 REM - COMPUTE PRINCIPAL
240 CLS: PRINT@9,"FIND PRINCIPAL"
230 PRINT@64,"ENTER MONTHLY PAYMENT";: INPUT R$
260 IF (VAL(R$)>0) AND (VAL(R$)<10000) THEN R=VAL(R$): GOTO280
270 PRINT@87,": GOTO250
280 GOSUB470
290 P=R*(((1+(I/12))^(Y*12)-1)/((I/12)*((1+(I/12))^(Y*12))))
300 P=INT(P*100): P$=STR$(P): L=LEN(P$)
310 PRINT@193,"PRINCIPAL="+LEFT$(P$,L-2)+"."+RIGHT$(P$,2)
320 GOSUB330
330 IF A$="R" THEN 100
340 GOTO230
330 REM - COMPUTE MONTHLY PAYMENT
360 CLS: PRINT@6,"FIND MONTHLY PAYMENT"
370 PRINT@64,"ENTER PRINCIPAL";: INPUT P$
380 IF (VAL(P$)>0) AND (VAL(P$)<10000000) THEN P=VAL(P$): GOTO400
390 PRINT@80,"": GOTO370
400 GOSUB470
410 R=P*(((I/12)*((1+(I/12))^(Y*12)))/((1+(I/12))^(Y*12)-1))
420 R=INT(R*100): R$=STR$(R): L=LEN(R$)
430 PRINT@193,"MONTHLY PAYMENT="+LEFT$(R$,L-2)+"."+RIGHT$(R$,2)
440 GOSUB330
430 IF A$="R" THEN 100
460 GOTO350
470 PRINT@97,"INTEREST RATE (% /YR)";: INPUT I$
480 IF (VAL(I$)>0) AND (VAL(I$)<91) THEN I=VAL(I$)/100: GOTO510
490 PRINT@117,"": GOTO470
510 PRINT@129,"NUMBER OF YEARS";: INPUT Y$
520 IF (VAL(Y$)>0) AND (VAL(Y$)<100) THEN Y=VAL(Y$): GOTO540
530 PRINT@146,"": GOTO310
540 RETURN
530 PRINT@416,"ENTER R FOR RESTART, OR JUST"
560 PRINT@448,"<ENTER> FOR SAME";: INPUT A$
570 IF NOT (A$="R" OR A$="") THEN PRINT@465,"": GOTO550
580 RETURN