This example was created to test the new string functionality.
Supports */+-() operators with precedence.
Also supports decimals and negation.
Code: Select all
1 REM Expression Evaluator by Gemino Smothers
2 REM Written in Express BASIC
5 CLS: PRINT "Expression Evaluator": PRINT: PRINT "Enter an expression.": PRINT
10 INPUT "Infix: ", infix$: IF LEN(infix$) THEN GOSUB 10000: PRINT "Evaluation: "; @(0)
30 PRINT: INPUT "Continue? (Y/N)", continue$: PRINT: continue$ = UCASE$(continue$)
40 IF continue$ = "N" THEN END
50 IF continue$ = "Y" THEN 10
60 GOTO 30
10000 postfix$ = "": operatorstack$ = "": GOSUB 14000
10010 FOR symbolpos = 1 TO LEN(infix$)
10020 symbol$ = MID$(infix$, symbolpos, 1)
10030 IF symbol$ = "." OR (ASC(symbol$) >= 48 AND ASC(symbol$) <= 57) THEN postfix$ = postfix$ + symbol$: GOTO 10080
10040 IF symbol$ = "(" THEN operatorstack$ = operatorstack$ + symbol$: GOTO 10080
10050 IF symbol$ = ")" THEN GOSUB 11000: GOTO 10080
10060 IF symbol$ = "*" OR symbol$ = "/" OR symbol$ = "+" OR symbol$ = "-" THEN GOSUB 12000
10070 IF symbol$ = "_" THEN postfix$ = postfix$ + "-"
10080 NEXT symbolpos
10090 newstack$ = ""
10100 FOR symbolpos = 1 TO LEN(operatorstack$)
10110 newstack$ = newstack$ + " " + MID$(operatorstack$, symbolpos, 1)
10120 NEXT symbolpos
10130 operatorstack$ = newstack$
10140 postfix$ = postfix$ + operatorstack$
10150 GOSUB 15000: RETURN
11000 postfix$ = postfix$ + " " + RIGHT$(operatorstack$, 1)
11010 operatorstack$ = LEFT$(operatorstack$, LEN(operatorstack$) - 1)
11020 IF RIGHT$(operatorstack$, 1) <> "(" THEN 11000
11030 operatorstack$ = LEFT$(operatorstack$, LEN(operatorstack$) - 1)
11040 RETURN
12000 GOSUB 13000
12010 IF LEN(operatorstack$) = 0 OR RIGHT$(operatorstack$, 1) = "(" OR symbolprecedence > stackprecedence THEN 12060
12020 postfix$ = postfix$ + " " + RIGHT$(operatorstack$, 1)
12030 operatorstack$ = LEFT$(operatorstack$, LEN(operatorstack$) - 1)
12040 GOSUB 13000
12050 IF LEN(operatorstack$) AND RIGHT$(operatorstack$, 1) <> "(" AND symbolprecedence <= stackprecedence THEN 12020
12060 operatorstack$ = operatorstack$ + symbol$
12070 postfix$ = postfix$ + " "
12080 RETURN
13000 stacktop$ = RIGHT$(operatorstack$, 1)
13010 IF stacktop$ = "+" OR stacktop$ = "-" THEN stackprecedence = 1: GOTO 13040
13020 IF stacktop$ = "*" OR stacktop$ = "/" THEN stackprecedence = 2: GOTO 13040
13030 stackprecedence = 0
13040 IF symbol$ = "+" OR symbol$ = "-" THEN symbolprecedence = 1: GOTO 13070
13050 IF symbol$ = "*" OR symbol$ = "/" THEN symbolprecedence = 2: GOTO 13070
13060 symbolprecedence = 0
13070 RETURN
14000 infix$ = "(" + infix$ + ")"
14010 FOR replacesymbol = 1 TO LEN(infix$)
14020 IF MID$(infix$, replacesymbol, 1) <> "-" THEN 14150
14030 symbol$ = MID$(infix$, replacesymbol - 1, 1)
14040 symbolpos = replacesymbol
14050 IF symbol$ <> " " THEN 14090
14060 symbolpos = symbolpos - 1
14070 symbol$ = MID$(infix$, symbolpos - 1, 1)
14080 IF symbol$ = " " THEN 14060
14090 negative = 0
14100 IF symbol$ = "(" OR symbol$ = "*" OR symbol$ = "/" OR symbol$ = "+" OR symbol$ = "-" THEN negative = 1
14110 IF NOT(negative) THEN 14150
14120 leftfix$ = LEFT$(infix$, replacesymbol - 1)
14130 infix$ = RIGHT$(infix$, LEN(infix$) - LEN(leftfix$) - 1)
14140 infix$ = leftfix$ + "_1*" + infix$
14150 NEXT replacesymbol
14160 RETURN
15000 @(0) = 0: pointer = 0
15010 IF INSTR(postfix$, " ") = 0 THEN symbol$ = postfix$: postfix$ = "": GOTO 15030
15020 symbol$ = LEFT$(postfix$, INSTR(postfix$, " ") - 1): postfix$ = RIGHT$(postfix$, LEN(postfix$) - LEN(symbol$) - 1)
15030 leftsymbol$ = LEFT$(symbol$, 1)
15040 IF NOT(leftsymbol$ = "." OR (ASC(leftsymbol$) >= 48 AND ASC(leftsymbol$) <= 57)) THEN 15050
15045 @(pointer) = VAL(symbol$): pointer = pointer + 1
15050 IF leftsymbol$ = "-" THEN GOSUB 16000
15060 IF leftsymbol$ = "*" OR leftsymbol$ = "/" OR leftsymbol$ = "+" THEN GOSUB 17000
15070 IF LEN(postfix$) THEN 15010
15080 RETURN
16000 IF LEN(symbol$) > 1 THEN 16050
16010 operator$ = symbol$
16020 pointer = pointer - 1: operand2 = @(pointer): @(pointer) = 0
16030 pointer = pointer - 1: operand1 = @(pointer): @(pointer) = 0
16040 GOSUB 18000: GOTO 16060
16050 @(pointer) = VAL(symbol$): pointer = pointer + 1
16060 RETURN
17000 operator$ = symbol$
17010 pointer = pointer - 1: operand2 = @(pointer): @(pointer) = 0
17020 pointer = pointer - 1: operand1 = @(pointer): @(pointer) = 0
17030 GOSUB 18000: RETURN
18000 IF operator$ = "*" THEN @(pointer) = operand1 * operand2
18010 IF operator$ = "/" THEN @(pointer) = operand1 / operand2
18020 IF operator$ = "+" THEN @(pointer) = operand1 + operand2
18030 IF operator$ = "-" THEN @(pointer) = operand1 - operand2
18040 pointer = pointer + 1: RETURN
