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Welcome to today's article. Today, you are going to learn how to detect palindromes from within your VB.NET application.
A palindrome is a word, phrase, or number which reads the same backward as forward. There are different types of palindromes, including the following:
- Characters and words
- Sentences and phrases
Characters and Words
Character palindromes read the same backward as forward. Noon, civic, radar, level, and kayak are good examples of character palindromes. Word-unit palindromes are palindromes in which the unit of reversal is simply the word. For example, the following is a word-unit palindrome: Blessed are they that believe that they are blessed.
Sentences and Phrases
Palindromic sentences consist of a sentence or phrase, for example: Live on time, emit no evil.
Some given names are palindromes, for example: Hannah, Anna, and Bob.
Semordnilap (palindromes spelled backward)—also known as: word reversals, reversible anagrams, heteropalindromes, or a semi-palindrome—spell a different word in reverse. For example: desserts, which is stressed backward, or vice versa.
In today's project, you will learn four different ways to identify a potential palindrome. Create a new Visual Basic Windows Forms project and design it as shown in Figure 1. You may give your objects different names than mine.
Figure 1: Design
Add the following code behind the button labeled 'Option 1':
Private Sub Button1_Click(sender As Object, e As EventArgs) _ Handles Button1.Click 'Option 1' Dim strText As String = TextBox1.Text strText = StrReverse(strText) If strText.Equals(strText) Then MessageBox.Show("Palindrome") Else MessageBox.Show("Not Palindrome") End If End Sub
This is relatively easy. It makes use of the built-in StrReverse string function to reverse the input; then, it simply compares the reversed string with the input string.
Add the following code for the button labeled 'Option 2':
Public Function Palindrome2(strText As String) As Boolean 'Option 2' Dim intCurr As Integer = 0 Dim intLength As Integer = strText.Length - 1 While intCurr < intLength If strText(intCurr) <> strText(intLength) Then Return False End If intCurr += 1 intLength -= 1 End While Return True End Function Private Sub Button2_Click(sender As Object, e As EventArgs) _ Handles Button2.Click MessageBox.Show(Palindrome2(TextBox1.Text)) End Sub
This method basically counts the letters from the front to the back, thus resulting in a True or False value.
Add 'Option 3':
Public Function Palindrome3(strText As String) As Boolean 'Option 3' Dim blnPal As Boolean = True For i As Integer = 0 To strText.Length \ 2 If strText(i) <> strText(strText.Length - i - 1) Then blnPal = False Exit For End If Next Return blnPal End Function Private Sub Button3_Click(sender As Object, e As EventArgs) _ Handles Button3.Click MessageBox.Show(Palindrome3(TextBox1.Text)) End Sub
Add the last method:
Private Function Palindrome4(ByVal strText As String, _ ByVal blnWhiteSpace As Boolean, _ ByVal blnCase As Boolean) As Boolean 'Option 4' Dim scCompare As StringComparison = If(blnCase, _ StringComparison.CurrentCultureIgnoreCase, _ StringComparison.CurrentCulture) If blnWhiteSpace Then Return String.Equals(strText.Replace(" ", String.Empty), _ String.Join("", strText.Replace(" ", String.Empty) _ .ToArray.Reverse), scCompare) Else Return String.Equals(strText, String.Join("", _ strText.ToArray.Reverse), scCompare) End If End Function Private Sub Button4_Click(sender As Object, e As EventArgs) _ Handles Button4.Click MessageBox.Show((Palindrome4(TextBox1.Text, True, True))) End Sub
Method 4 caters to Whitespace and case sensitivity, if needed.
The code for this article is available on GitHub.
Palindromes can be tricky. Languages can be tricky. Hopefully, with this article you have learned how to properly manipulate strings to check for palindromes.