计算字符串中特定字符出现次数的最简单方法是什么？
也就是说，我需要写一个函数countTheCharacters()，这样
str = "the little red hen"
count = countTheCharacters(str,"e") ' Count should equal 4
count = countTheCharacters(str,"t") ' Count should equal 3
【问题讨论】：
最直接的就是简单地遍历字符串中的字符：
Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer
Dim cnt As Integer = 0
For Each c As Char In value
If c = ch Then
cnt += 1
End If
Next
Return cnt
End Function
用法：
count = CountCharacter(str, "e"C)
另一种几乎同样有效且代码更短的方法是使用 LINQ 扩展方法：
Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer
Return value.Count(Function(c As Char) c = ch)
End Function
【讨论】：
For i as Integer = 0 to value.Length - 1 而不是 For Each 循环来提高 10% 左右。
'Count' is not a member of 'String'.
Count 方法是IEnumerable<T> 的扩展方法，String 实现了IEnumerable<char>。如果您收到类似的编译器错误，则说明您缺少页面顶部的 using System.Linq; 引用。
Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer Dim cnt As Integer For Each c In value If c = ch Then cnt = cnt + 1 End If Next CountCharacter = cnt End Function
这是最简单的方法：
text = "the little red hen"
count = text.Split("e").Length -1 ' Equals 4
count = text.Split("t").Length -1 ' Equals 3
【讨论】：
SplitStringOptions.RemoveEmptyEntries 作为第二个参数传递给 Split()
你可以试试这个
Dim occurCount As Integer = Len(testStr) - Len(testStr.Replace(testCharStr, ""))
【讨论】：
Len(testCharStr) 和Ceil 它也适用于字符串的出现。
这是一个简单的版本。
text.count(function(x) x = "a")
上面会给你字符串中a的数量。如果你想忽略大小写：
text.count(function(x) Ucase(x) = "A")
或者如果你只是想数字母：
text.count(function(x) Char.IsLetter(x) = True)
试一试！
【讨论】：
或者（在 VB.NET 中）：
Function InstanceCount(ByVal StringToSearch As String,
ByVal StringToFind As String) As Long
If Len(StringToFind) Then
InstanceCount = UBound(Split(StringToSearch, StringToFind))
End If
End Function
【讨论】：
Ujjwal Manandhar 的代码到 VB.NET 的转换如下...
Dim a As String = "this is test"
Dim pattern As String = "t"
Dim ex As New System.Text.RegularExpressions.Regex(pattern)
Dim m As System.Text.RegularExpressions.MatchCollection
m = ex.Matches(a)
MsgBox(m.Count.ToString())
【讨论】：
谢谢，@guffa。在 .NET 中，在一行甚至更长的语句中执行此操作的能力非常方便。这个 VB.NET 示例计算 LineFeed 字符的数量：
Dim j As Integer = MyString.Count(Function(c As Char) c = vbLf)
j 返回 MyString 中 LineFeed 的数量。
【讨论】：
我认为这是最简单的：
Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer
Return len(value) - len(replace(value, ch, ""))
End Function
【讨论】：
Public Class VOWELS
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim str1, s, c As String
Dim i, l As Integer
str1 = TextBox1.Text
l = Len(str1)
c = 0
i = 0
Dim intloopIndex As Integer
For intloopIndex = 1 To l
s = Mid(str1, intloopIndex, 1)
If (s = "A" Or s = "a" Or s = "E" Or s = "e" Or s = "I" Or s = "i" Or s = "O" Or s = "o" Or s = "U" Or s = "u") Then
c = c + 1
End If
Next
MsgBox("No of Vowels: " + c.ToString)
End Sub
End Class
【讨论】：
当我找到这个解决方案时，我正在寻找一些稍微不同的东西，因为我想要计算的字符串比一个字符长，所以我想出了这个解决方案：
Public Shared Function StrCounter(str As String, CountStr As String) As Integer
Dim Ctr As Integer = 0
Dim Ptr As Integer = 1
While InStr(Ptr, str, CountStr) > 0
Ptr = InStr(Ptr, str, CountStr) + Len(CountStr)
Ctr += 1
End While
Return Ctr
End Function
【讨论】：
使用正则表达式...
Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer
Return (New System.Text.RegularExpressions.Regex(ch)).Matches(value).Count
End Function
【讨论】：
Public Function CountOccurrences(ByVal StToSerach As String, ByVal StToLookFor As String) As Int32
Dim iPos = -1
Dim iFound = 0
Do
iPos = StToSerach.IndexOf(StToLookFor, iPos + 1)
If iPos <> -1 Then
iFound += 1
End If<br/>
Loop Until iPos = -1
Return iFound
End Function
代码用法：
Dim iCountTimes As Integer = CountOccurrences("Can I call you now?", "a")
您也可以将其作为扩展：
<Extension()> _
Public Function CountOccurrences(ByVal StToSerach As String, ByVal StToLookFor As String) As Int32
Dim iPos = -1
Dim iFound = 0
Do
iPos = StToSerach.IndexOf(StToLookFor, iPos + 1)
If iPos <> -1 Then
iFound += 1
End If
Loop Until iPos = -1
Return iFound
End Function
代码用法：
Dim iCountTimes2 As Integer = "Can I call you now?".CountOccurrences("a")
【讨论】：
我建议你这样做：
String.Replace("e", "").Count
String.Replace("t", "").Count
您也可以分别使用.Split("e").Count - 1 或.Split("t").Count - 1，但如果您在String 的开头有e 或a，则会给出错误的值。
【讨论】：
eCount = str.Length - Replace(str, "e", "").Length
tCount = str.Length - Replace(str, "t", "").Length
【讨论】：
另一种可能性是使用拆分：
Dim tmp() As String
tmp = Split(Expression, Delimiter)
Dim count As Integer = tmp.Length - 1
【讨论】：
我用的是LINQ，解决方法很简单：
C# 中的代码：
count = yourString.ToCharArray().Count(c => c == 'e');
函数中的代码：
public static int countTheCharacters(string str, char charToCount){
return str.ToCharArray().Count(c => c == charToCount);
}
调用函数：
count = countTheCharacters(yourString, 'e');
【讨论】：
这么简单的东西有多大的代码：
在 C# 中，创建扩展方法并使用 LINQ。
public static int CountOccurences(this string s, char c)
{
return s.Count(t => t == c);
}
用法：
int count = "toto is the best".CountOccurences('t');
结果：4。
【讨论】：
我找到了最佳答案 :P :
String.ToString.Count - String.ToString.Replace("e", "").Count
String.ToString.Count - String.ToString.Replace("t", "").Count
【讨论】：
var charCount = "string with periods...".Count(x => '.' == x);
【讨论】：
我使用以下功能。它不是最节省内存的，但很容易理解，支持多种比较方法，只有 4 行，速度很快，也主要在 VBA 中工作，不仅可以找到单个字符，还可以找到任何搜索字符串（我经常搜索 VbCrLf (s))。
唯一缺少的是从不同的“开始”开始搜索的能力
Function inStC(myInput As String, Search As String, Optional myCompareMethod As Long = CompareMethod.Text) As Long
If InStr(1, myInput, Search, myCompareMethod) = 0 Then Return 0
Return UBound(Split(myInput, Search,, myCompareMethod))
End Function
我喜欢的一点是它使用例子很紧凑。
str="the little red hen"
count=inStC(str,"e") 'count should equal 4
count=inStC(str,"t") 'count should equal 3
当我在这里时，我想对我的 inStB 函数进行调整，它不会返回字符串的计数，而是在搜索字符串存在时简单地返回一个布尔值。我经常需要这个函数，这让我的代码更干净。
Function inStB(myInput As String, Search As String, Optional Start As Long = 1, Optional myCompareMethod As Long = CompareMethod.Text) As Boolean
If InStr(Start, myInput, Search, myCompareMethod) > 0 Then Return True
Return False
End Function
【讨论】：
另一种可能是使用正则表达式：
string a = "this is test";
string pattern = "t";
System.Text.RegularExpressions.Regex ex = new System.Text.RegularExpressions.Regex(pattern);
System.Text.RegularExpressions.MatchCollection m = ex.Matches(a);
MessageBox.Show(m.Count.ToString());
请将其转换为 VB.NET。
【讨论】：
用途：
Function fNbrStrInStr(strin As Variant, strToCount As String)
fNbrStrInStr = UBound(Split(strin, strToCount)) - LBound(Split(strin, strToCount))
End Function
我使用strin 作为变体来处理很长的文本。根据用户设置，分割可以是从零开始，也可以是从低端开始，减去它可以确保正确的计数。
为了保持代码简洁，我没有对 strcount 长于 strin 进行测试。
【讨论】：
' Trying to find the amount of "." in the text
' if txtName looks like "hi...hi" then intdots will = 3
Dim test As String = txtName.Text
Dim intdots As Integer = 0
For i = 1 To test.Length
Dim inta As Integer = 0 + 1
Dim stra As String = test.Substring(inta)
If stra = "." Then
intdots = intdots + 1
End If
Next
txttest.text = intdots
【讨论】：
Private Sub Data_KeyPress(sender As Object, e As KeyPressEventArgs) Handles Data.KeyPress
If Not IsNumeric(e.KeyChar) And Not e.KeyChar = ChrW(Keys.Back) And Not e.KeyChar = "." Then
e.Handled = True
Else
If e.KeyChar = "." And Data.Text.ToCharArray().Count(Function(c) c = ".") > 0 Then
e.Handled = True
End If
End If
End Sub
【讨论】：
用途：
Dim a
inputString = InputBox("Enter String", "Enter Value", "")
MyString = UCase(inputString)
MsgBox MyString
Dim stringLength
stringLength = Len(MyString)
Dim temp
output = ""
i = 1
Do
temp = Mid(MyString, i, 1)
MsgBox temp & i
CharacterCount = len(MyString) - len(Replace(MyString, temp, ""))
MyString = Replace(MyString, temp, "")
output = output & temp & ": " & CharacterCount & vbNewline
Loop While MyString <> ""
MsgBox output
【讨论】：
Explicit Off 和 Option Strict Off。
这是解决OP问题的直接代码：
Dim str As String = "the little red hen"
Dim total As Int32
Dim Target As String = "e"
Dim Temp As Int32
Dim Temp2 As Int32 = -1
Line50:
Temp = str.IndexOf(Target, Temp2 + 1)
Temp2 = Temp
If Temp <> -1 Then
' Means there is a target there
total = total + 1
GoTo Line50
End If
MessageBox.Show(CStr(total))
现在，这是一个解决 OP 问题的方便函数：
Public Function CountOccurrence(ByVal YourStringToCountOccurrence As String, ByVal TargetSingleCharacterToCount As String) As Int32
Dim total As Int32
Dim Temp As Int32
Dim Temp2 As Int32 = -1
Line50:
Temp = YourStringToCountOccurrence.IndexOf(TargetSingleCharacterToCount, Temp2 + 1)
Temp2 = Temp
If Temp <> -1 Then
' Means there is a target there
total = total + 1
GoTo Line50
Else
Return total
End If
End Function
函数使用示例：
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
Dim str As String = "the little red hen"
MessageBox.Show(CStr(CountOccurrence(str, "e")))
' It will return 4
End Sub
【讨论】：
GOTOs !