/***********************************************************
eval.c -- 式の評価
***********************************************************/
#console
Declare Function printf CDECL Lib"msvcrt" (fmt As *Byte, ...) As Long
Declare Function getchar CDECL Lib"msvcrt" () As Long
Declare Function isdigit CDECL Lib"msvcrt" (c As Long) As Long
Declare Function cexit CDECL Lib"msvcrt" Alias "exit" (c As Long) As Long
Dim ch As Long
Sub error(s As *Byte) /* エラー処理 */
printf(Ex"%s\n", s): cexit(1)
End Sub
Sub readch() /* 1文字を読む. 空白は読み飛ばす. */
Do
ch = getchar()
If (ch = -1) Then Exit Sub
Loop while (ch = Asc(Ex" ") Or ch = Asc(Ex"\t"))
End Sub
Function number() As Double /* 数 */
Dim x As Double, a As Double
Dim sign As Long
If (ch = Asc(Ex"+") Or ch = Asc(Ex"-")) Then
sign = ch: readch()
End If
If (isdigit(ch) = 0) Then error(Ex"数か '(' がありません")
x = ch - Asc(Ex"0")
while (1)
readch()
If isdigit(ch) <> 0 Then
x = 10 * x + ch - Asc(Ex"0")
Else
Exit While
End If
Wend
if (ch = Asc(Ex".")) Then
a = 1
while (1)
readch()
If isdigit(ch) <> 0 Then
a = a / 10
x = x + (a) * (ch - Asc(Ex"0"))
Else
Exit While
End If
Wend
End If
If (sign = Asc(Ex"-")) Then number = -x Else number = x
End Function
Function factor() As Double /* 因子 */
Dim x As Double
If (ch <> Asc(Ex"(Ex")) Then
factor = number()
Exit Function
End If
readch(): x = expression()
If (ch <> Asc(Ex")")) Then error(Ex"')' がありません")
readch(): factor = x
End Function
Function term() As Double /* 項 */
Dim x As Double, y As Double
x = factor()
While (1)
If (ch = Asc(Ex"*")) Then
readch(): x = x * factor()
Else If (ch = Asc(Ex"/")) Then
readch(): y = factor()
If (y = 0) Then error(Ex"0 では割れません")
x = x / y
Else
Exit While
End If
Wend
term = x
End Function
Function expression() As Double /* 式 */
Dim x As Double
x = term()
While (1)
If (ch = Asc(Ex"+")) Then
readch(): x = x + term()
Else if (ch = Asc(Ex"-")) Then
readch(): x = x - term()
Else
Exit While
End If
Wend
expression = x
End Function
Sub main()
Dim x As Double
readch(): x = expression()
If (ch <> Asc(Ex"\n")) Then error(Ex"文法の間違いがあります")
printf(Ex"%g\n", x)
End Sub
main()
