主题：如何用分数形式显示计算结果

output.show(Fract(eval(1-999/7999)))

 

上面的结果为：7/8，而不是7000/7999。

 

请问能精确显示吗？

 不可能精确显示，电脑不会运算分数，除非自己编程实现。

 说说你要的需求，然后根据需求帮你弄弄。

初中学生的作业中有很多含分数的算式，家长每晚要检查签名，如果每道题都核算一遍，头都大了。希望在软件中输入含分数算式，结果用分式表示。

由于电脑计算时以小数形式进行计算，最后转换为分数，所以结果出现误差，上面的要求感觉很难实现。

想办法弄成这样：output.show((7999-999) & "/" & 7999)

 下面的代码，只支持一个分数的加减操作。

 如果要实现楼主想要的分数计算，就必须自己去实现eval()函数，对表达式进行提取，分析，运算。比较麻烦......涉及递归，操作符比较。

 也就是说，让电脑按照人的顺序去运算，很费精力……楼主请高手帮忙哈。

Dim data As String = "10/5+(5-2/10)+4"
Dim catchs As New System.Text.RegularExpressions.Regex("[\+\-\*/\(\)]*\d+")
Dim mc As System.Text.RegularExpressions.MatchCollection = catchs.Matches(data)
Dim maxfm As Double = 1
Dim nums(mc.count - 1) As String
Dim fzs(mc.count - 1) As String

catchs = New System.Text.RegularExpressions.Regex("^[\+\-\*/\(]+")
Dim mc0 As System.Text.RegularExpressions.MatchCollection = catchs.Matches(mc(0).Value)
If mc0.Count = 0 Then
    nums(0) = "+" & mc(0).Value
Else
    nums(0) = mc(0).Value
End If
Dim m, n, r As Double
For i As Integer = 1 To mc.Count - 1
    nums(i) = mc(i).Value
    If nums(i).IndexOf("/") <> -1 Then
        catchs = New System.Text.RegularExpressions.Regex("\d+")
        Dim mc2 As System.Text.RegularExpressions.MatchCollection = catchs.Matches(nums(i))
        Dim right As Integer = mc2(0).Value
        '求最小公倍数
        If right > maxfm Then
            m = right
            n = maxfm
        Else
            m = maxfm
            n = right
        End If
        Do
            r = m Mod n
            If r = 0 Then Exit Do
            m = n
            n = r
        Loop
        maxfm = maxfm * right / n    
    End If
Next
Dim Index As Integer = 0
For i As Integer = 0 To nums.Length - 1
    catchs = New System.Text.RegularExpressions.Regex("[^\d]+")
    Dim mc2 As System.Text.RegularExpressions.MatchCollection = catchs.Matches(nums(i))
    Dim left As String = mc2(0).Value
    catchs = New System.Text.RegularExpressions.Regex("\d+")
    Dim mc3 As System.Text.RegularExpressions.MatchCollection = catchs.Matches(nums(i))
    Dim right As Integer = mc3(0).Value  
    If nums(i).IndexOf("/") = -1 Then   '如果不是分母
        fzs(Index) = left & right * maxfm
        Index = Index + 1
    Else
        catchs = New System.Text.RegularExpressions.Regex("[^\d]+")
        Dim mc4 As System.Text.RegularExpressions.MatchCollection = catchs.Matches(fzs(Index - 1))
        Dim last_left As String = mc4(0).Value
        catchs = New System.Text.RegularExpressions.Regex("\d+")
        Dim mc5 As System.Text.RegularExpressions.MatchCollection = catchs.Matches(fzs(Index - 1))
        Dim last_right As Double = mc5(0).Value
        fzs(Index - 1) = last_left & last_right / right
    End If
Next

Dim fz As String = ""
For i As Integer = 0 To fzs.Length - 1
    fz = fz & fzs(i)
Next
Dim num As String = ""
For i As Integer = 0 To nums.Length - 1
    num = num & nums(i)
Next
fz = fz & data.SubString(num.Length - 1)
fz = eval(fz)

'约分
If fz > maxfm Then
    m = fz
    n = maxfm
Else
    m = maxfm
    n = fz
End If
Do
    r = m Mod n
    If r = 0 Then Exit Do
    m = n
    n = r
Loop
fz = fz / n
Dim fm As Integer = maxfm / n
Dim result As String = fz & "/" & fm
Output.Show(result)

用得着那么复杂吗？

 

Dim s As String = "355/555"
Dim a As Integer = s.split("/")(0) '分子数
Dim b As Integer = s.split("/")(1)  '分母数
Dim c As Integer =  Math.Min(a,b)
If a > 1 And b > 1
    For i As Integer = c To 2 Step -1
        If b Mod i = 0 And a Mod i = 0
            Output.show(a/i & "/" & b/i )
            Exit For
        End If
        If i = 2
            Output.show(a & "/" & b)
        End If
    Next
End If

哦，我看错了楼主的意思，以为仅仅是约分呢！按照楼主的要求出现1-这样的情况，这样即可，同时实现自动约分：

 

Dim s As String = "1-999/7999"
Dim s1 As String
Dim a As Integer = s.split("/")(1) - s.split("/")(0).split("-")(1)
Dim b As Integer = s.split("/")(1)  '分母数
Dim c As Integer =  Math.Min(a,b)
If a > b
    s = a \ b & "-"
Else
    s = Nothing
End If
If a > 1 And b > 1
    For i As Integer = c To 2 Step -1
        If b Mod i = 0 And a Mod i = 0
            Output.show(s & a/i & "/" & b/i )
            Exit For
        End If
        If i = 2
            Output.show(a & "/" & b)
        End If
    Next
End If

 

 

祝各位中秋节快乐！辛苦了。

 

如果给定的算式是含分数、整数、连除的混合运算，这个设置还是比较复杂，学习中。

复杂在于分解公式，其他的并不可怕，您可以将不同的复杂公式贴出来，让大家在摸索中寻找规律！

综合测试题：-4*25/2/5/10*(-1)*1-1/600+5*5*5/125*(1/5+(-1/5))+1/600-41/7999-(-41/7999)-999/7999