Evaluate Mathematical Expression From User Input String?

May 19, 2010

I am making a simple calculator that will evaluate functions I have a entry box and the user types in simple equations i.e. 1+4*3/5=? how would i make this evaluate the string?


Evaluating Mathematical Expression In A String?

Jul 7, 2011

Is there a method that allows me to evaluate a mathematical expression in a string? Example (Not actual Code):

Input = "2+2"
Output = SomeMethod(Input)
Output = 4

Update: Nevermind, I found a way around it by using DataTable.Compute.

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Mar 29, 2009

i want to make a program in which the user can input a mathematical function so the program can then work with it. So the user would input something like x^4+x+2 and then an x and the program would calculate f(x). What i don't know is how to let the user input the function.

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What Data Type Will Allow The User To Input 0 And Allow The Mathematical Functions To Work Properly

Mar 29, 2011

I am currently using double data types. The problem I am encountering is that sometimes the user will have to input a value of 0 in the required text box and this creates an error. My question is what data type will allow the user to input 0 and allow the mathematical functions to work properly. Decimals maybe?

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Oct 12, 2009

I am trying to create a procedure which will evaluate a string expression as if it were a line of code...Kind of like what a graphing calculator does when you enter a formula. Does anyone have any experience with this in VB? I have an example of C++ code which uses CodeDom, but I am a bit rusty with my C++!

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Regular Expression That Checks Input String

Oct 26, 2009

I understand the concept of regular expressions but I am looking for a regular expression string that checks the input string for the following criteria only...
1.) Upper and lower case letters
2.) The space character
3.) Apostrophe
4.) Comma
5.) Period
6.) Hyphen

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Apr 24, 2012

I am using a class to check for certain words in my application to prevent SQL Injection. In the class, there is a for loop that tries to match a specific word with the words from a blacklist. If there is a match, I must redirect to the system's error page. However, when a match is found and I try to redirect, I keep getting the error "Unable to evaluate expression."


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Feb 10, 2009

I have this line in some

Integer.TryParse(ThisRow.Item("DatumID").ToString, n)

ThisRow is a datarow. The "DatumID" in this case happens to be an empty string, but is not Null. When I break on this line, and try to evaluate it by highlighting it and pressing Shift+F9, I get the message "Unable to evaluate expression". Interestingly, it is actually evaluating correctly (since the item holds an empty string, TryParse returns False).

I have tested this in every way I could think of (mostly I thought I had left out a parenthesis in my expression, but that wasn't true). So why won't that expression evaluate when tested, even though it is actually working correctly?

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Jun 5, 2010

"In what circumstances will the following boolean expression evaluate to true?

strAlphabet.indexOf(StrCharacter) >= 0 And _
strAlphabet.indexOf(StrCharacter) < 0

Once you have answered that question, you should be able to complete this description: the expression indicates whether strCharacter is ..... but is not...."

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Oct 24, 2011

I have one test class which having few variables declared in the header of the class where it will be accessed for all the subroutines and functions in the class. Here's the sample of my declaration:

Private m_dblMaxPwrLimit As Double
Private m_dblMaxPower As Double
Private m_intHalfPwrIndex As Short
Private m_intMaxPwrIndex As Short

After that, I have one Private Function which need to access some of the variables declare in above. Part of my function is show as below:

Private Function GetPmaxIndex(ByVal Serial As Short) As Boolean
Dim i As Short
Dim Total As Short


The problem is when I step into the line of m_dblMaxPower and m_intMaxPwrIndex, I can't see the value of these variables which is suppose I can see it as in VB6. Additionally, when I put Add Watch for these variables, it showed 'unable to evaluate expression'. I guess it is not being used and I think something is wrong with my declaration but I do not how should I declare it corretly because as for VB6, we can declare all the variables in the header of the class and we can use it for all the subroutine/function within the class.

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Oct 15, 2008

In debug mode I get into a line that evaluates to false because the expression cannot be evaluated because of "Cannot evaluate expression because the code of the current method is optimized." Program does not assert or error out. If Item.Length then . . . (Here when I hover the mouse it displays "Cannot evaluate expression because the code of the current method is optimized"). What interesting is that it only occurs in one of .vb files.BTW, I'm programming in Compact Framework.

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May 8, 2010

I am developing an application that takes user input into text boxes or list boxes or check boxes.  I have 4 forms with questions of different categories.  I want to form a paragraph string with some literal string text and add in the text from text boxes, selected item from list boxes and, either,  add literal text string or add nothing to the string based on check box condition.dim strScopeParagraph as string

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Mar 9, 2012

I simply just to declare a variable as a string that is = to the user's input, and I thought that was done by this:

dim xxx as string =("skdlfjaofhhwa")

But it's not working?

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May 22, 2012

Dim MyString as String = "Various very long strings, 1000 of lines. Here \n \n \n to <TR> here."
Dim MyMatch As MatchCollection
MyMatch = Regex.Matches(MyString, "Here((.|\n|\r)*?)<\/TR>", RegexOptions.Multiline)
Dim MyArray(MyMatch.Count - 1)

This code stalls. I was trying to find out why my app stalls, and never breaks, or reports an error. I found out, that it stalls in the last line of code, where Count in MyMatch sometimes is not numeric. It has various error values, such as: "Unable to evaluate expression", "Evaluation of expression or statement timed out", and similar.I was trying to find solution, searching the internet, but no success. On MSDN site, there are 2 simple advice: a.) Verify that the entered code is correct. b.) Simplify your expression so that it takes less time to execute.My code is correct. It works on some strings, and stalls on other. I couldn't simplify it more, because strings to test with matches are different every time. They differ in length, and also in content

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Oct 12, 2010

I am trying to write following expression on a datacolumn. But it results in error:Replicate('*', nLevel) + NameWhere: Replicate() is a user defined function (in a module). nLevel and Name are two other columns in same data table.

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Jun 22, 2010

My app has text boxes to accept input from user to questions shown on labels. When the user input is valid, a literal is added to a string incorporating the user input. If the user doesn't input anything or if user inputs "no" or "None" I want the literal and the user input to not add to my string. Make any sense? See my code below:


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Aug 24, 2009

I have an LLBLGen Pro project which has generated VB.Net 2.0 Self Servicing code.I have a function to return a list of custom structures based on a search using the generated code.I would like to supply a Dictionary of FieldNames and Values to this function and for each one add a new Predicate Expression to the search.How can I check the String within the dictionary that represents the Field name and work out which EntityField to add the Predciate Expression for?

Dim dbFiles As New AllFilesCollection
Dim dbFilter As New PredicateExpression
If Not String.IsNullOrEmpty(ClientName) Then


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Jul 15, 2010

[code] please help me how to get and/or evaluate object from this json string with VB.Net.

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May 17, 2012

I have a string like this:Correct Strings Dim value As String = "45, 2111,56, 1, 9, 99, 62,"Invalid Strings:Dim value As String = "10.01, 12,, , "I need to evaluate this string that has this format indefinitely,The regex evaluate the commas who are in series and are only integers.

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May 4, 2012

I have one text box that the user enters an integer into. I use a select case to determine what the length of the number is. (along w/ string.length, etc)based on how long it is, I can determine if the number is 1-9, 10-99, 100-999, etc. What I want to do next is, evaluate the number and display a roman numeral that matches.

intMyNumber.substring(1,?) ' 1 would return the leftmost number
if intMyNumber.substring(1,?) = 1 then
if intMyNumber.substring(2,?) = 1 then 'etc


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Feb 1, 2011

I'm wondering how to evaluate an expression using the assert object. The idea is to check if a string is longer then what is minimally acceptable. For example, Assert.AreEqual(stringName.length, >5). I know this method doesn't work but the concept is what I'm trying to get across. Is there a way to test this?

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Jan 15, 2011

I need some help with the input validation of my application. Attached is the code that I have written as well as a screenshot of the front end. I specifically need input validation to verify that the user selected input for cbLengthOfStay is a number between 1-10 as well as input validation to verify the user input for txtMedication, txtSurgicalCharges, txtLabFees and txtRehabilitation is a positive numerical number. Please feel free to critique my attached code. [Code]

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Feb 19, 2012

If my Category and Forum selection is incorrect I am sorry and feel free to move it. I'd like to have the users input in the message box that will show. For example: There is a textbox and the user puts in their name as Bob. Then the message box would be: What my main goal is, is being able to include the users input they type inside the textbox inside the message box.

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May 24, 2011

I have a WCF application, written in VB.NET that takes a generic Dictionary(Of String, String) as one of the parameters.When I pass in a Key/Value pair that has a backslash as one of the characters in the value, the client automatically changes the entire value to Nothing or in the XML it shows this:

<Value i:nil="true />

Is there some special way to escape backslashes when passing them in a string to a WCF service? As far as I know the backslash isn't a reserved character in XML.

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Jan 19, 2012

I'm currently coding a ASP.NET web application using VB.NET. I'd like to know how to limit the input of the regular expression validator to numbers only (with specific number of digits e.g 7-20 digits).

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Nov 3, 2011

Option Strict On Public Class Form1 Private Sub btnDistance_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDistance.Click 'The btnEnterSpeed click event accepts and displays up to ten speeds from the user'and then calculates and displays average speed


I cannot figure out how to incorporate the number of days into the input box then get it to loop and count the number of times the User inputs in the number of days. Then I have to incorporate it into the equation to get the total distance D = MPH * Hours. What I have right now wil not count up the number of days and locks up after I input one number and will not add anything to the listbox. Because I also have to make sure that they cant add nonnumaric values and the number of hours per day cannot exceed 20. I have put things in and taken them out but it has been 2 days and I am lost now

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Regular Expression To Check Input On Multiline Textbox?

Apr 22, 2011

Lets say I have a multiline textbox that I would like to have checked for say, 1-2 digits over a max of 5 lines. I found a regular expression pattern answered on another similar question on here but it was not working for me even after modifying it a number of times.

I'm currently using the following without success.

Dim textCheck As New Regex("(^d{1,2}$
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Jun 20, 2012

I'm having a few problems converting some code into VB.NET from C#. Most of the translating is done, but I am getting errors when I try to run my code, and I can't figure out what is causing them. Here is the Sub I translated.

Public Sub CreateWidget()
Dim blue As LCDColor
blue.Red = 0
blue.Green = 0


The error I receive on this line ("vision.Widgets.CreateWidget(wg1)") reads "In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user."

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Jun 6, 2009

I receive a System.Data.SqlClient.SqlException in the following code: Specifically Incorrect syntax near ' In order to evaluate an indexed property, the property must be qualified and the arguments must be explicitly supplied by the user. The exception detail in its entirety is shown below the code.


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Mar 15, 2011

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I am in a need of a Regular Expression to restrict input to only certain characters in a text box. The text box can only allow 0 or 1 "+" sign at the beginning and at no other position. The text box can only allow 0 or 1 ":" sign not before the "+" sign. The text box can allow any number of 0-9 digits.


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Feb 5, 2010

I must convert string data from a CNC that is arithmetic expression to a number that I can use in a VB application that I wrote. The following is what I get out of the cnc. [18722*65536+19377]/67108864. I need to evaluate this expression in my VB ap. The format of the string is not always the same as what I have illustrated.

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Jul 14, 2009

I'm trying to save what the user types in the vb code Dim user as Inputbox("") for example in a .txt file i can save the textbox and listbox but i cnt figure out how to save the inputbox i really need this to be saved the most.

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Feb 11, 2011

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Nov 3, 2009

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The thing i have done this before ,count that is. I know you cant average strings and some other function but i have been able to count.

d Dim comm As New OleDb.OleDbCommand("Select * From " & Me.OpenFileDialog1.SafeFileName & " Where Status  <> 'S'", con)
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Jun 23, 2011

I need a regular expression that can validate that a string is an alphanumeric comma delimited string.


123, 4A67, GGG, 767 would be valid.
12333, 78787&*, GH778 would be invalid
fghkjhfdg8797< would be invalid

This is what I have so far, but isn't quite right: ^(?=.*[a-zA-Z0-9][,]).*$

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Sep 17, 2010

I want to use "*" or "" as mathematical operators as such:


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Oct 11, 2010

I have a little question about application settings. I have a regular expression in my code which should be customizable by the user so I made an application setting for it.  The regular expression is used in a class in the project and has the following value

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myMatch As

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Mar 15, 2009

We know that VB string start and end with double quotes " "

So we have to use "" if we want " in VB string.

I wonder if there is a regular expression pattern which will match VB string?.

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