Function VAL (X) In UCSD PASCAL For Apple II

Michael Erperstorfer Vienna, Austria

Function VAL (X) is similar to BASIC'S VAL-function:

X must be a string of an integer number;

VAL returns a true integer number;

If X is no integer number VAL returns 0;

String X may have leading or trailing spaces.

PROGRAM VALTEST;
VAR INPUT : STRING;
FUNCTION VAL (S : STRING) : INTEGER; VAR START, I, LEN, O, V : INTEGER; NEG : BOOLEAN;
BEGIN
V : = 0;
NEG: = FALSE;
WHILE COPY (S, l, l) = ’ ’ DO S : = COPY (S, 2, LENGTH (S)-l);
(* remove blanks from left *)
WHILE COPY (S, LENGTH(S),1) = ’ ’ DO S : = COPY
(S, l, LENGTH (S)-l);
(* remove blanks from right *)
START : = 1;
IF COPY (S, 1,1) = ’-’ THEN BEGIN
START: = 2;
NEG: = TRUE END;
(* if first char = ’-’ *)
(* number is negative *)
(* increment start value *)
(* to skip ’-’ sign *)
(* set neg-flag *)
LEN: = LENGTH (S);
FOR I: = START TO LEN DO BEGIN
O: = ORD(S[I]);
IF (O > 47) AND (O < 58) THEN
(*check if char is number *)
V : = V + TRUNC (PWROFTEN (LEN-I)) * (O-48)
(* calculate value *)
ELSE BEGIN
(* if char is not number *)
VAL: = 0;
(* set value to 0 *)
EXIT (VAL)
(* and exit function *)
END
END;
IF NEG THEN VAL: = -V ELSE VAL: = V
END;
BEGIN REPEAT WRITE (’ STRING : ’);
READLN (INPUT);
WRITELN (’ = ’, VAL (INPUT))
UNTIL INPUT = ’ ’
END.