用于制作简单计算器的 Visual Basic 帮助答案

【问题标题】：Visual Basic Help for making a simple calculator用于制作简单计算器的 Visual Basic 帮助
【发布时间】：2018-12-06 04:17:06
【问题描述】：

编写一个名为CalculateResult 的函数过程，该过程执行请求的操作并返回一个十进制值。此函数应接受以下参数： decOperand1 As Decimal - 为第一个操作数输入的值。 strOperator As String - 这四个运算符之一：+、-、* 或 /。 decOperand2 As Decimal - 为第二个操作数输入的值。

这是我需要编写的代码，任何可以提供的帮助将不胜感激

【问题讨论】：

欢迎来到 SO。我建议先阅读 tour，然后阅读 How to Ask 和 Minimal, Complete, and Verifiable example，了解 SO 的工作原理以及如何有效地提问。
对我来说像家庭作业

标签： calculator basic

【解决方案1】：

可能的编码方案：

REM Code a Function procedure named CalculateResult that performs the
REM requested operation and returns a decimal value. This function should
REM accept the following parameters: decOperand1 As Decimal - The value
REM entered for the first operand. strOperator As String - One of these
REM four operators: +, -, *, or /. decOperand2 As Decimal - The value
REM entered for the second operand.
PRINT "Enter value1";: INPUT decOperand1&
PRINT "Enter operand(+,-,*,/,^)";: INPUT strOperator$
PRINT "Enter value2";: INPUT decOperand2&
PRINT "Result"; CalculateResult(decOperand1&, strOperator$, decOperand2&)
END
FUNCTION CalculateResult (decOperand1&, strOperator$, decOperand2&)
    SELECT CASE strOperator$
        CASE "+", "+="
            CalculateResult = decOperand1& + decOperand2&
        CASE "-", "-="
            CalculateResult = decOperand1& - decOperand2&
        CASE "*", "*="
            CalculateResult = decOperand1& * decOperand2&
        CASE "/", "/="
            CalculateResult = decOperand1& / decOperand2&
        CASE "^", "^="
            CalculateResult = decOperand1& ^ decOperand2&
        CASE ELSE
            PRINT "Unknown operator."
    END SELECT
END FUNCTION

【讨论】：

例如“10 * (20 - 1)”是什么？

【解决方案2】：

附加解析功能：

REM Code a Function procedure named CalculateResult that performs the
REM requested operation and returns a decimal value. This function should
REM accept the following parameters: decOperand1 As Decimal - The value
REM entered for the first operand. strOperator As String - One of these
REM four operators: +, -, *, or /. decOperand2 As Decimal - The value
REM entered for the second operand.
PRINT "Enter value1";: INPUT decOperand1&
PRINT "Enter operand(+,-,*,/,^)";: INPUT strOperator$
PRINT "Enter value2";: INPUT decCalc2$
IF decCalc2$ = "" THEN
    PRINT "Result:"; CalculateResult2(decOperand1&, strOperator$)
ELSE
    decOperand2& = VAL(decCalc2$)
    PRINT "Result:"; CalculateResult(decOperand1&, strOperator$, decOperand2&)
END IF
END
FUNCTION CalculateResult (decOperand1&, strOperator$, decOperand2&)
    SELECT CASE strOperator$
        CASE "+", "+="
            CalculateResult = decOperand1& + decOperand2&
        CASE "-", "-="
            CalculateResult = decOperand1& - decOperand2&
        CASE "*", "*="
            CalculateResult = decOperand1& * decOperand2&
        CASE "/", "/="
            CalculateResult = decOperand1& / decOperand2&
        CASE "^", "^="
            CalculateResult = decOperand1& ^ decOperand2&
        CASE ELSE
            PRINT "Unknown operator."
    END SELECT
END FUNCTION
FUNCTION CalculateResult2 (decOperand1&, strOperator$)
    SELECT CASE strOperator$
        CASE "++"
            CalculateResult2 = decOperand1& + 1&
        CASE "--"
            CalculateResult2 = decOperand1& - 1&
        CASE "//" ' shift-left
            CalculateResult2 = decOperand1& * 2&
        CASE "**" ' shift-right
            CalculateResult2 = decOperand1& / 2&
        CASE ELSE
            PRINT "Unknown operator."
    END SELECT
END FUNCTION

【讨论】：

【解决方案3】：

这是 QB45、QB64 中成熟的递归下降解析器：

REM File: Recursive descent parser 2019.

DIM SHARED Out2 AS STRING
DIM SHARED Token AS INTEGER
DIM SHARED Token1 AS STRING
DIM SHARED Token2 AS STRING
DIM SHARED Token.Index AS INTEGER

DO
    COLOR 15, 0
    PRINT "Equation";: INPUT Out2
    IF Out2 = "" THEN EXIT DO
    COLOR 14, 0
    PRINT "Equals:"; Equate(Out2)
LOOP
COLOR 7, 0
END

FUNCTION Equate (Out2$)
    Temp# = DFalse
    Var = INSTR(Out2$, " ")
    WHILE Var
        Out2$ = LEFT$(Out2$, Var - 1) + MID$(Out2$, Var + 1)
        Var = INSTR(Out2$, " ")
    WEND
    IF Out2$ <> "" THEN
        Out2$ = UCASE$(Out2$)
        Token.Index = 1
        CALL Get.Token
        CALL Parse1(Temp#)
    END IF
    Equate = Temp#
END FUNCTION

' logical parser
SUB Parse1 (Temp#)
    CALL Parse2(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "|", "&", "~", "?", ":"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse2(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' relational parser
SUB Parse2 (Temp#)
    CALL Parse3(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "<", ">", "=", "#", ">=", "<=", "<>", "^="
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse3(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' addition/subtraction parser
SUB Parse3 (Temp#)
    CALL Parse4(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "+", "-"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse4(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' modulo parser
SUB Parse4 (Temp#)
    CALL Parse5(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "%"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse5(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' integer division parser
SUB Parse5 (Temp#)
    CALL Parse6(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "\"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse6(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' multiplication/division parser
SUB Parse6 (Temp#)
    CALL Parse7(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "*", "/"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse7(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' power parser
SUB Parse7 (Temp#)
    CALL Parse7a(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "^"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        CALL Parse7a(Temp2#)
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' dual-unary parser
SUB Parse7a (Temp#)
    CALL Parse8(Temp#)
    Token.Parsed$ = Token2$
    DO
        SELECT CASE Token.Parsed$
            CASE "<<", ">>", "--", "++", "**", "//", "||", "##", "^^"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        Token.Stored$ = Token1$
        CALL Get.Token
        '    CALL Parse8(Temp2#) ' no secondary token
        Token1$ = Token.Stored$
        CALL Arith(Token.Parsed$, Temp#, Temp2#)
        Token.Parsed$ = Token2$
    LOOP
END SUB

' not/unary plus/unary negative parser
SUB Parse8 (Temp#)
    Token.Negate$ = "" ' reset token storage
    Token.Parsed$ = Token2$ ' store token
    ' process token
    DO
        SELECT CASE Token.Parsed$
            CASE "!", "-", "+", "--", "++"
                Eat$ = ""
            CASE ELSE
                EXIT DO
        END SELECT
        CALL Get.Token ' read next token
        Token.Negate$ = Token.Negate$ + Token.Parsed$
        Token.Parsed$ = Token2$ ' store token
    LOOP
    CALL Parse9(Temp#) ' get next operator
    ' process the combined operators
    FOR Token.Type = LEN(Token.Negate$) TO 1 STEP -1
        SELECT CASE MID$(Token.Negate$, Token.Type, 1) ' get next token
            CASE "+"
                Eat$ = ""
            CASE "-"
                Temp# = -Temp# ' perform negate
            CASE "!" ' not
                Temp# = NOT Temp# ' perform not calculation
        END SELECT
    NEXT
END SUB

SUB Parse9 (Temp#)
    SELECT CASE Token
        CASE 1
            SELECT CASE Token2$
                CASE "("
                    CALL Get.Token
                    IF Token2$ <> ")" THEN
                        DO
                            CALL Parse1(Temp#)
                        LOOP UNTIL Token2$ = ")" OR Token = False
                        CALL Get.Token
                    END IF
                CASE ")"
                    CALL Get.Token
                    EXIT SUB
            END SELECT
        CASE 2
            SELECT CASE RIGHT$(Token2$, 1)
                CASE "H" ' hexidecimal
                    Temp# = DFalse
                    Var = False
                    FOR Var1 = LEN(Token2$) - 1 TO 1 STEP -1
                        Var2 = VAL("&H" + (MID$(Token2$, Var1, 1)))
                        Temp# = Temp# + Var2 * 16 ^ Var
                        Var = Var + 1
                    NEXT
                CASE "O" ' octal
                    Temp# = DFalse
                    Var = False
                    FOR Var1 = LEN(Token2$) - 1 TO 1 STEP -1
                        Var2 = VAL(MID$(Token2$, Var1, 1))
                        Temp# = Temp# + Var2 * 8 ^ Var
                        Var = Var + 1
                    NEXT
                CASE "B" ' binary
                    Temp# = DFalse
                    Var = False
                    FOR Var1 = LEN(Token2$) - 1 TO 1 STEP -1
                        IF MID$(Token2$, Var1, 1) = "1" THEN
                            Temp# = Temp# + 2 ^ Var
                        END IF
                        Var = Var + 1
                    NEXT
                CASE ELSE ' decimal
                    Temp# = VAL(Token2$)
            END SELECT
            CALL Get.Token
        CASE 3
            SELECT CASE Token2$
                CASE "RND"
                    Temp# = RND
                CASE "ABS"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = ABS(Temp#)
                CASE "NOT"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = NOT (Temp#)
                CASE "SGN"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = SGN(Temp#)
                CASE "SQR"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = SQR(Temp#)
                CASE "OR"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Number# = Temp#
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = Number# OR Temp#
                CASE "AND"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Number# = Temp#
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = Number# AND Temp#
                CASE "EQV"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Number# = Temp#
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = Number# EQV Temp#
                CASE "IMP"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Number# = Temp#
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = Number# IMP Temp#
                CASE "MOD"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Number# = Temp#
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = Number# MOD Temp#
                CASE "XOR"
                    CALL Get.Token
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Number# = Temp#
                    CALL Get.Token
                    CALL Parse1(Temp#)
                    Temp# = Number# XOR Temp#
            END SELECT
            CALL Get.Token
    END SELECT
END SUB

SUB Arith (Token.Parsed$, Temp#, Temp2#)
    SELECT CASE Token.Parsed$
        CASE "+"
            Temp# = Temp# + Temp2#
        CASE "-"
            Temp# = Temp# - Temp2#
        CASE "/"
            Temp# = Temp# / Temp2#
        CASE "\"
            Temp# = Temp# \ Temp2#
        CASE "*"
            Temp# = Temp# * Temp2#
        CASE "^"
            Temp# = Temp# ^ Temp2#
        CASE "<"
            Temp# = Temp# < Temp2#
        CASE ">"
            Temp# = Temp# > Temp2#
        CASE "<<"
            Temp# = Temp# * 2#
        CASE ">>"
            Temp# = Temp# \ 2#
        CASE "||"
            Temp# = Temp# * 10#
        CASE "##"
            Temp# = Temp# \ 10#
        CASE "^^"
            Temp# = Temp# ^ 10#
        CASE "++"
            Temp# = Temp# + 1#
        CASE "--"
            Temp# = Temp# - 1#
        CASE "**"
            Temp# = Temp# ^ 2#
        CASE "//"
            Temp# = SQR(Temp#)
        CASE "="
            Temp# = Temp# = Temp2#
        CASE "<="
            Temp# = Temp# <= Temp2#
        CASE ">="
            Temp# = Temp# >= Temp2#
        CASE "#", "<>"
            Temp# = Temp# <> Temp2#
        CASE "^="
            Temp# = Temp# ^ Temp2#
        CASE "|"
            Temp# = Temp# OR Temp2#
        CASE "&"
            Temp# = Temp# AND Temp2#
        CASE "%"
            Temp# = Temp# MOD Temp2#
        CASE "~"
            Temp# = Temp# XOR Temp2#
        CASE "?"
            Temp# = Temp# IMP Temp2#
        CASE ":"
            Temp# = Temp# EQV Temp2#
    END SELECT
END SUB

SUB Get.Token
    Token.List$ = " -+*/\^()[]{}<>=#|&!%~?:,"
    Token2$ = ""
    Token = False
    IF Token.Index > LEN(Out2) THEN
        Token2$ = ""
        EXIT SUB
    END IF
    CALL Get.Token2(Token.Exists)
    IF Token.Exists THEN
        EXIT SUB
    END IF
    Token.Element$ = MID$(Out2, Token.Index, 1)
    IF LEN(Token.Element$) THEN
        IF INSTR(Token.List$, Token.Element$) THEN
            Token = 1
            Token2$ = Token.Element$
            Token.Index = Token.Index + 1
            EXIT SUB
        END IF
    END IF
    Token.Element$ = MID$(Out2, Token.Index, 1)
    IF (Token.Element$ >= "0" AND Token.Element$ <= "9") OR Token.Element$ = "." THEN
        DO
            IF LEN(Token.Element$) = False THEN
                EXIT DO
            END IF
            IF INSTR(Token.List$, Token.Element$) THEN
                EXIT DO
            END IF
            Token2$ = Token2$ + Token.Element$
            Token.Index = Token.Index + 1
            Token.Element$ = MID$(Out2, Token.Index, 1)
        LOOP
        Token = 2
        EXIT SUB
    END IF
    Token.Element$ = MID$(Out2, Token.Index, 1)
    IF Token.Element$ >= "A" AND Token.Element$ <= "Z" THEN
        DO
            IF LEN(Token.Element$) = False THEN
                EXIT DO
            END IF
            IF INSTR(Token.List$, MID$(Out2, Token.Index, 1)) THEN
                EXIT DO
            END IF
            Token2$ = Token2$ + Token.Element$
            Token.Index = Token.Index + 1
            Token.Element$ = MID$(Out2, Token.Index, 1)
        LOOP
        Token = 3
        EXIT SUB
    END IF
END SUB

' tokens of length 2
SUB Get.Token2 (Token.Exists)
    Token.Exists = False
    Next.Token$ = MID$(Out2, Token.Index, 2)
    SELECT CASE Next.Token$
        CASE "||"
            Token = 1
            Token2$ = "||"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "##"
            Token = 1
            Token2$ = "##"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "<<"
            Token = 1
            Token2$ = "<<"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE ">>"
            Token = 1
            Token2$ = ">>"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "--"
            Token = 1
            Token2$ = "--"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "++"
            Token = 1
            Token2$ = "++"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "**"
            Token = 1
            Token2$ = "**"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "//"
            Token = 1
            Token2$ = "//"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE ">=", "=>"
            Token = 1
            Token2$ = ">="
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "<=", "=<"
            Token = 1
            Token2$ = "<="
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "<>", "><"
            Token = 1
            Token2$ = "<>"
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "^="
            Token = 1
            Token2$ = "^="
            Token.Index = Token.Index + 2
            Token.Exists = True
        CASE "^^"
            Token = 1
            Token2$ = "^^"
            Token.Index = Token.Index + 2
            Token.Exists = True
    END SELECT
END SUB

【讨论】：