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?

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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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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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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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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...
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3.) Apostrophe
4.) Comma
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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."

[Code]....

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Feb 10, 2009

I have this line in some

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

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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

[code]....

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

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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:

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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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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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[Code]...

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Aug 24, 2009

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

[code].....

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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 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

[code]....

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Feb 1, 2011

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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

[Code]...

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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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}$
?
?){0,5}", RegexOptions.Multiline)

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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

[code]....

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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.

[Code]...

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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.

[Code]...

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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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[CODE]...

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Examples:

123, 4A67, GGG, 767 would be valid.
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fghkjhfdg8797< would be invalid

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

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

[code...]

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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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So now I made a new Settings file in my project and gave the following value for this string in the settings file: ^([w-]+(?:.[w-]+)*)@((?:[w-]+.)*w[w-]{0,66}).([a-z]{2,6}(?:.[a-z]{2})?)$ [URL]

So when i do this in Visual Studio 2008, Visual Studio automatically creates a app.config xml file with the right settings in it. But when I start my application and use the regular expression like this:

Dim

myMatch As

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If

[CODE]...

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

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

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how can I use a string ( string = "my.resources.imagename" ) as an expression? like this:

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is this possible? if yes, how then? I searched all over the internet but I couldn't find it

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Dec 29, 2011

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Required:

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Not required but nice:

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Sep 28, 2011

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dim con as new oledbconnection
dim cmd as new oledbcommand
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[code]....

everything is done,, such as opening the connection and defining teh data reader, etc as you can see from teh code(which was derived from another question but i made edits to suit my use for it)I also have problems with checking wether a user is online. obviously i will be referring to the table to do that using something like

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[code]....

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Feb 17, 2010

Does anybody know of a call in vb.net that will evaluate a string expression. For example, how would one evaluate the expression "(1+2)*(3+4)"?I've looked all over and it seems that people are writing their own parsers. There has to be a better way. After all these years, VB.Net must have something that will take an expression and evaluate it.

Dim strMyExpression as string = "(1+2)*(3+4)"
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and the result would be 35.Also, when will microsoft start to use google as the search engine for these forums? Bing really sucks. Searching for "Evaluating a string expression in VB.net" gives the most bizarre links.

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