'===========================================================================
' Subject: STRING MATH                       Date: 10-31-95 (16:01)       
' Author:  Joe Krzton                        Code: QB, QBasic, PDS        
' Origin:  FidoNet QUIK_BAS Echo           Packet: ALGOR.ABC
'===========================================================================
DECLARE FUNCTION Add$ (o1$, o2$)
DECLARE SUB AlignDot (x1$, x2$)
DECLARE FUNCTION Subtract$ (o1$, o2$)
DEFDBL A-Z
b = 1.5: c = 0
DO
    b = b + c * 16
    pi = pi + 4 / b
    PRINT pi; : LOCATE , 1
    c = c + 1
LOOP UNTIL INKEY$ = CHR$(27)
END

DEFINT A-Z
FUNCTION Add$ (o1$, o2$)
op1$ = o1$: op2$ = o2$
IF LEFT$(op1$, 1) = "-" THEN s1 = -1:  ELSE s1 = 1
IF INSTR("+-", LEFT$(op1$, 1)) > 0 THEN op1$ = MID$(op1$, 2)
IF LEFT$(op2$, 1) = "-" THEN s2 = -1:  ELSE s2 = 1
IF INSTR("+-", LEFT$(op2$, 1)) > 0 THEN op2$ = MID$(op2$, 2)

IF s1 = -1 AND s2 = 1 THEN Add$ = Subtract$(op2$, op1$): EXIT FUNCTION
IF s1 = 1 AND s2 = -1 THEN Add$ = Subtract$(op1$, op2$): EXIT FUNCTION
pfx$ = "": IF s1 = -1 THEN pfx$ = "-"

AlignDot op1$, op2$
out$ = "": carry = 0

FOR z = LEN(op1$) TO 1 STEP -1
    IF MID$(op1$, z, 1) <> "." THEN
        ans = VAL(MID$(op1$, z, 1)) + VAL(MID$(op2$, z, 1)) + carry
        IF out$ <> "" OR (ans MOD 10) > 0 THEN out$ = CHR$(48 + (ans MOD 10)) + out$
        carry = INT(ans / 10)
    ELSE
        out$ = "." + out$
    END IF
NEXT z

IF RIGHT$(out$, 1) = "." THEN out$ = LEFT$(out$, LEN(out$) - 1)
IF carry > 0 THEN out$ = CHR$(48 + carry) + out$
Add$ = pfx$ + out$
END FUNCTION

DEFSNG A-Z
SUB AlignDot (x1$, x2$)
IF INSTR(x1$, ".") = 0 THEN x1$ = x1$ + ".0"
IF INSTR(x2$, ".") = 0 THEN x2$ = x2$ + ".0"
da1 = INSTR(x1$, ".")
da2 = INSTR(x2$, ".")
IF da1 < da2 THEN x1$ = STRING$(da2 - da1, "0") + x1$
IF da1 > da2 THEN x2$ = STRING$(da1 - da2, "0") + x2$
IF LEN(x1$) > LEN(x2$) THEN x2$ = x2$ + STRING$(LEN(x1$) - LEN(x2$), "0")
IF LEN(x2$) > LEN(x1$) THEN x1$ = x1$ + STRING$(LEN(x2$) - LEN(x1$), "0")
END SUB

FUNCTION Subtract$ (o1$, o2$)
END FUNCTION