VB.NET Stack Type
Use the Stack type to push and pop elements at the top of a collection.Stack. A Stack adds elements to its top. Elements are pushed to the top, and then popped from the top. We see how to loop over a VB.NET Stack, push and pop elements, and also peek and count.
QueueLIFO: The last element added to the Stack is the first element removed from the Stack. All activity occurs on the top of the stack.
Example. This example shows how to repeatedly Push elements to the top of a Stack. Then, we use the For-Each loop to display the Stack in the order from first to last. The most recently added element (1000) is at the top of the Stack.
For Each, For VB.NET program that uses Stack
Module Module1
Sub Main()
Dim stack As Stack(Of Integer) = New Stack(Of Integer)
stack.Push(10)
stack.Push(100)
stack.Push(1000)
' Display stack elements.
For Each value As Integer In stack
Console.WriteLine(value)
Next
End Sub
End Module
Output
1000
100
10
Example 2. This example introduces the Pop and Peek functions on the Stack. With Pop, you take the top element off of the Stack and it is stored in the return value. It is no longer is part the Stack.
Peek: With Peek, you take the top element and copy it to the return value, but it is not removed.
Count: To avoid exceptions with an empty stack, use the Count property and test it against zero.
VB.NET program that uses Pop and Peek
Module Module1
Sub Main()
Dim stack As Stack(Of Integer) = New Stack(Of Integer)
stack.Push(10)
stack.Push(100)
stack.Push(1000)
' Test Pop.
Dim value As Integer = stack.Pop
Console.WriteLine("Element popped: {0}", value)
' Test Peek.
value = stack.Peek
Console.WriteLine("Element peeked: {0}", value)
End Sub
End Module
Output
Element popped: 1000
Element peeked: 100
Example 3. In this example, we show how to copy an array into a new Stack. Please note that the types of the two collections must match. The array of Strings must be copied to a Stack of Strings.
String ArrayNext: We use the Contains function, which works in much the same way as the List Contains function. It returns True or False.
List VB.NET program that uses Stack constructor and Contains
Module Module1
Sub Main()
Dim array(2) As String
array(0) = "dot"
array(1) = "net"
array(2) = "perls"
' Copy array to a new stack.
Dim stack As Stack(Of String) = New Stack(Of String)(array)
' Use Contains.
Console.WriteLine(stack.Contains("net"))
Console.WriteLine(stack.Contains("not"))
End Sub
End Module
Output
True
False
Summary. The Stack collection can be used to implement certain parsers that track nesting levels, such as HTML parsers. As each nested element is encountered, a new element is added to the Stack.
Note: Stacks are useful in any system where the most recently added element is the most urgent.
Thus: The VB.NET Stack type is used to implement a variety of important algorithms.
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