Yesterday i had a look at how to set values of variables from nummbers stored in external txt files
the variables then needed to be added up so i used trial and error first
((XVAL) + (NEWVAL))
assuming that XVAL was set to 10 and NEWVAL was set to 20 i expected to get the answer of thirty but waqs presented with the new value of 10 20
VB.net pysicaly added the two values together but i wanted the mathematical product of the two which is ((10) + (20)) = 30
yep its a newb question could anyone explain how to achieve what im affter
XVAL and NEWVAL are strings, so they are simply being concatenated together. You need to convert them to integers, so that VB.NET will treat them as such. To do this, use the Int32.Parse() method.
Dim intXVAL As Integer = Int32.Parse(XVAL)
Dim intNEWVAL as Integer = Int32.Parse(NEWVAL)
Dim result = intXVAL + intNEWVAL
You want to cast them to a number first.
Try CDbl.
See http://msdn.microsoft.com/en-us/library/Aa263426 for more.
edit: Oops, thought you were talking about VBA.
Try using Double.Parse(YOURVALUE) if you're talking about VB.NET.
Have you tried the Val() function?
Val(XVAL) + Val(NEWVAL)
The + operator in VB.NET (for backwards-compatibility reasons) means both add and concatenate depending on the types of the variables it is being used with. With two numeric types (Integer, Single, Double, etc.), it adds the values together as you would expect. However, with String types, it concatenates the two strings.
Presumably, then, your XVAL and NEWVAL variables are String types because they're being read out of a text file, which is causing VB.NET to concatenate them into a new string instead of add them together. To get the behavior you're expecting, you need to convert them to numeric types.
Some of the other answers suggest casting simply casting the string values to numeric types (CInt, CSng, CDbl, etc.), but this may not work as expected if the value contained by your string cannot be converted to number. The Int32.Parse method will throw an exception if the value held by your string cannot be represented as a number. This is especially important to keep in mind if you're reading values from a text file that are not guaranteed to adhere to any particular constraints.
Instead, you probably want to use something like Int32.TryParse, which returns a Boolean value indicating whether or not the conversion succeeded and will not throw an exception.
As you are reading from a text file I assume that you are reading your values out as strings, so when you do this:
((XVAL) + (NEWVAL))
It is effectively concatenating the two strings together. In order to get the mathematical product of the two values these need to be int/integers which is the number type.
There are a number of ways you can do this, but in essence you have to 'cast' the strings to ints and then do your calculation.
So in vb.net it would be something like this (pseudo code):
Dim xval As String = "10"
Dim newval As String = "20"
Dim x As Integer = Int32.Parse(xval)
Dim n As Integer = Int32.Parse(newval)
Dim prod As Integer = x + n
Console.WriteLine(prod)
There are a number of other methods of doing this, for example using:
int.Parse(...)
or
Integer.TryParse(...)
More information on these sorts of type conversions can be found here:
http://dotnetperls.com/integer-parse-vbnet
One thing to bear in mind with these sorts of conversions is that you have to be certain that your input data is convertable. Otherwise your code will throw exceptions. This is where TryParse is useful as you can use this to check the inputs and handle invalid inputs without the need for exceptions.
Related
Here is what i have tried so far , but no new shot variable is being declared
Module Module1
Dim shotlist As New List(Of Boolean)
Dim shono As Integer = 0
Dim shonos As String
Dim shotname As String
Dim fshot As Boolean
Dim shots As String
Sub Main()
For i As Integer = 0 To 1000
Dim ("shots" & i) as String = "shots" & i
fshot = Convert.ToBoolean(shots)
Next
End Sub
End Module
You can't do things this way. The variable names you see when you write a program are lost, turned into memory addresses by the compiler when it compiles your program. You cannot store any information using a variable's name - the name is just a reference for you, the programmer, during the time you write a program (design time)
Think of variables like buckets, with labels on the outside. Buckets only hold certain kinds of data inside
Dim shotname as String
This declares a bucket labelled shotname on the outside and it can hold a string inside. You can put a string inside it:
shotname = "Shot 1"
You can put any string you like inside this bucket, and thus anything you can reasonably represent as a string can also be put inside this bucket:
shotname = DateTime.Now.ToString()
This takes the current time and turns it into a string that looks like a date/time, and puts it in the bucket. The thing in the bucket is always a string, and lots of things (nearly anything actually) can be represented as a string, but we don't type all our buckets as strings because it isn't very useful - if you have two buckets that hold numbers for example, you can multiply them:
Dim a as Integer
a=2
Dim b as Integer
b=3
Dim c as Integer
c=a*b
But you can't multiply strings, even if they're strings trust look like numbers; strings would have to be converted to numbers first. Storing everything as a string and converting it to some other type before working on it then converting it back to a string to store it would be very wearisome
So that's all well and good and solves the problem of storing varying information in the computer memory and giving it a name that you can reference it by, but it means the developer has to know all the info that will ever be entered into the program. shotname is just one bucket storing one bit of info. Sure you could have
Dim shotname1 as String
Dim shotname2 as String
Dim shotname3 as String
But it would be quite tedious copy paste exercise to do this for a thousand shotname, and after you've done it you have to refer to all of them individually using their full name. There isn't a way to dynamically refer to bucket labels when you write a program, so this won't work:
For i = 0 To 1000
shotname&i = "This is shotname number " & i
Next i
Remember, shotname is lost when compiling, and i is too, so shotname&i just flat out cannot work. Both these things become, in essence, memory addresses that mean something to the compiler and you can't join two memory addresses together to get a third memory address that stores some data. They were only ever nice names for you to help you understand how to write the program, pick good names and and not get confused about what is what
Instead you need the mechanism that was invented to allow varying amounts of data not known at the design-time of the program - arrays
At their heart, arrays are what you're trying to do. You're trying to have load of buckets with a name you can vary and form the name programmatically.
Array naming is simple; an array has a name like any other variable (what I've been calling a bucket up to now - going to switch to calling them variables because everyone else does) and the name refers to the array as a whole, but the array is divided up into multiple slots all of which store the same type of data and have a unique index. Though the name of the array itself is fixed, the index can be varied; together they form a reference to a slot within the array and provide a mechanism for having names that can be generated dynamically
Dim shotnames(999) as String
This here is an array of 1000 strings, and it's called shotnames. It's good to use a plural name because it helps remind you that it's an array, holding multiple something. The 999 defines the last valid slot in the array - arrays start at 0, so with this one running 0 to 999 means there are 1000 entries in it
And critically, though the shotnames part of the variable name remains fixed and must be what you use to refer to the array itself(if you want to do something with the entire thing, like pass it to a function), referring to an individual element/slot in the array is done by tacking a number onto the end within brackets:
shotnames(587) = "The 588th shotname"
Keep in mind that "starts at 0 thing"
This 587 can come from anything that supplies a number; it doesn't have to be hard coded by you when you write the program:
For i = 0 to 999
shotnames(i) = "The " & (i+1) & "th shotname"
Next i
Or things that generate numbers:
shotnames(DateTime.Now.Minute) = "X"
If it's 12:59 when this code runs, then shotnames(59), the sixtieth slot in the array, will become filled with X
There are other kinds of varying storage; a list or a dictionary are commonly used examples, but they follow these same notions - you'll get a variable where part of the name is fixed and part of the name is an index you can vary.
At their heart they are just arrays too- if you looked inside a List you'd find an array with some extra code surrounding it that, when the array gets full, it makes a new array of twice the size and copies everything over. This way it provides "an array that expands" type functionality - something that arrays don't do natively.
Dictionaries are worth mentioning because they provide a way to index by other things than a number and can achieve storage of a great number of things not known at design time as a result:
Dim x as New Dictionary(Of String, Object)
This creates a dictionary indexed by a string that stores objects (I.e. anything - dates, strings, numbers, people..)
You could do like:
x("name") = "John"
x("age") = 32
You could even realize what you were trying to do earlier:
For i = 0 to 999
x("shotname"&i) = "The " & (i+1) & "th shotname"
Next i
(Though you'd probably do this in a Dictionary(Of string, string), ie a dictionary that is both indexed by string and stores strings.. and you probably wouldn't go to this level of effort to have a dictionary that stores x("shotname587") when it's simpler to declare an array shotname(587))
But the original premise remains true: your variable has a fixed part of the name (ie x) and a changeable part of the name (ie the string in the brackets) that is used as an index.
And there is no magic to the indexing by string either. If you opened up a dictionary and looked inside it, you'd find an array, together with some bits of code that take the string you passed in as an index, and turn it into a number like 587, and store the info you want in index 587. And there is a routine to deal with the case where two different strings both become 587 when converted, but other than that it's all just "if you want a variable where part of the name is changeable/formable programmatically rather than by the developer, it's an array"
I'm experimenting with learning how conversions work between variable types. Right now, I'm looking at using one conversion inside a Try/Catch (for values that can't convert). Is there a way to have a string representation of a value (obtained from a TextBox), convert it to a test type, and then see how that converts to all the other VB standard types in a loop? Or even better if there is a resource that already does this.
I can do this, but the code is very close to being repetitive and I'm hoping for a loop of some kind to simplify and shorten it.
First of all, there is no such thing as variable type in VB.net. May be you confusing with object variables - but this is not the same thing
Dim o As Object
o = 1 ' integer
The type that is stored in o is still integer. It is boxed.
Dim i As Integer = CInt(o)
You just un-boxed it. It works because object is lowest of types and all other derive from it. So, it can "box" any other type.
In UI we use text boxes to collect data. Text boxes can contain only string. And unless you writing these strings to a file like txt or xml you usually need to convert these strings to a type you use in application.
Dim port as Integer = Convert.ToInt32(txtPort.Text)
This is not really the area where you can determine, what type is in that text box. You really need to know upfront - what are you expecting there? You can test your text for being one type or another by using
Integer.TryParse
Date.TryParse
.....TryParse
.............
But the thing is, some data can successfully pass this test fro multiple types.
Good question. While it is possible to declare variables of type type and use them in a loop, these cannot be used in declarations or DirectCast.
Dim types() As Type = {GetType(Integer), GetType(Double)}
Dim testType As Type = GetType(Double)
The easiest way might be to test each value individually something like this (although you'll probably want a try-catch for each or all the items).
Dim xInteger As Integer
xInteger = TextBox1.Text
s &= "Integer: " & xInteger.ToString & vbcrlf ' or some test
Dim xDouble As Double
xDouble = TextBox1.Text
s &= "Double" & ": " & xDouble.ToString & vbcrlf
...
I'm trying to create a function which generates a secret encoded message. It takes in three things: a string, for example, "testingtestingonetwothree", as well as the desired number of characters, for example 5, and the desired number of words, for example 5. It generates the message by starting at the first character, and extracting every fifth character through the string, putting these characters into a codeword, then starting at the second character and extracting every fifth character through the string, putting these into a second codeword, and so on. It just outputs a string, with the codewords separated by a space. So for this example it would produce: "tntnt egieh stntr tegwe isooe".
I'm okay at coding but new to VBA. I've made what I think is a valid function, but when it's used in the spreadsheet I get a #VALUE! error: "A value used in the formula is the wrong data type". This is the user defined function I made:
Function encode(strng, numchars, numwords)
Dim word As Integer
Dim step As Integer
Dim temp As String
Dim output As String
For word = 1 To numchars
step = word
temp = ""
Do While step <= Len(strng)
temp = temp & Mid(strng, 1, step)
step = step + numchars
Loop
If word = 1 Then output = temp Else output = output & " " & temp
Next word
encode = output
End Function
And when it's used in the spreadsheet I just call it, as in
=encode(A16,A7,A10)
Where A16 contains testingtestingonetwothree, A7 contains 5 and A10 contains 5.
Does my function seem okay? And is there anything you guys can see which could be giving the value error? Any help would be greatly appreciated, thanks a lot for reading.
EDIT: This now outputs a value, but the wrong value. It outputs: "ttestintestingtesttestingtestingontestingtestingonetwot tetestingtestingtestitestingtestingonetestingtestingonetwoth ", when it should output: "tntnt egieh stntr tegwe isooe". Is there anything you guys can see that my function is doing wrong?
EDIT2: After fixing the Mid function, to
temp = temp & Mid(strng, step, 1)
as per vacip's answer, the function now produces the correct answer.
Ok, everyone says it works, but for me, it doesn't produce the desired output. What the...???
Anyway, I think your Mid function is in the wrong order, try it like this:
temp = temp & Mid(strng, step, 1)
Also, make sure to properly declare your variables, like this:
Function encode(strng As String, numchars As Integer, numwords As Integer) As String
I have also rewritten your IF statement, that one-line thing is strange for me...
If word = 1 Then
output = temp
Else
output = output & " " & temp
End If
This way it worked for me.
Other people have addressed the type problem. Here is a different suggestion. The cipher that you are describing is a simple transposition cipher, specifically a columnar transposition ( https://en.wikipedia.org/wiki/Transposition_cipher#Columnar_transposition )
The way people did this pre-computer was to write the characters into a grid row by row then read them off column by column. In fact -- this is probably still the easiest way to implement it even with computers. Declare a variant which can be redimensioned to be an array with e.g. 5 columns (where 5 is the skip between letters) and the number of rows is chosen to be large enough so that the grid can hold the string. After you load up the characters row by row, read them off column by column using nested for loops.
Once you get a basic example working, you can try to implement a version which uses a key to determine the order that you read off the columns for added security.
Coding classical cryptography/cryptanalysis as an excellent way to learn a programming language. Almost the first thing I do when I try to learn a new language is to implement a Vigenere cipher in it. Even though it is long out of print and can be somewhat tricky to translate to modern dialects of Basic the book "Cryptanalysis for Microcomputers" by Caxton Foster is great fun and can be purchased for just a few dollars from online used bookstores.
You need to define your Function's type. So in this case I believe you would want
Function encode(strng, numchars, numwords) As String
I tested your code exactly as it is, and it worked fine.
So, your problem may be:
A certain argument of your function is not the right type. (I bet the len method is the problem in there).
Check if A16 is really a string. If not, consider converting it to a string before if you want to pass numbers too:
Function encode(strng as variant, numchars as integer, numwords as integer) as string
strng = str(strng)
Check also if A7 and A10 are really integers.
I'm developing a system that shows the total amount paid of a student from the database. For some students that only have a few transactions the function below gives an error Conversion from string "" to type double... but if a student doesn't have any data entry or the values are zero-to-many the code below encounters it. What should I do? Do I need to adjust the code? Please help.
I have here an Function that gets the total items.
Function Totalpaid() As Double
Dim i As Integer
For i = 0 To ((tbl_receipt.Items.Count) - 1)
Totalpaid = (Totalpaid + tbl_receipt.Items(i).SubItems(3).Text)
Next
End Function
You're trying to add two numbers but one of the operands is not a number. You're assuming that the Text of the subitem will be converted a number and added to the running total. At least one of your subitems is blank though. Maybe you consider that to represent zero but it doesn't. It doesn't represent any number at all so the operation fails.
What you should be doing is validating and converting the subitem contents yourself and then providing the system with two Double values to add. If there is no value then you either ignore that subitem or use zero explicitly. Option Strict On will at least force you to perform the conversion but it's still up to you to provide the validation if there's any chance that the data will not be valid.
To me this looks like a problem with your data rather than the code directly. I would recommend sanitising your data before trying to use it in a calculation, i.e.:
Function Totalpaid() As Double
Dim i As Integer
Dim val as Double
For i = 0 To ((tbl_receipt.Items.Count) - 1)
If Double.TryParse(tbl_receipt.Items(i).SubItems(3).Text, val) Then
Totalpaid = (Totalpaid + val)
End If
Next
Return Totalpaid
End Function
The message Conversion from string "" to type double... is saying that your are trying to convert an empty string to a Double which cannot work.
As a side note, when testing your code I did have to include the line Return Totalpaid, I don't know if this was missed when you where writing out the question.
I am a very novice VB.NET programmer. How do I convert one type to another?
Dim a as String="2"
Dim b as Integer='what?
There are several ways to convert a string to an integer.
You know the string contains a numeric:
Dim b as Integer = Integer.Parse(a)
If it is not a valid integer or contains non numerals, it can crash. Other value types (Decimal, Double) have the same method.
Pretty much the same:
Dim b as Integer= Convert.ToInt32(b)
You dont know if the string is clean or not. For instance this would be used to convert a value from a text box, where the user types "cat" as their age:
If Integer.TryParse(a, b) Then ...
The big difference here is that the return is a Boolean (True or False) telling you whether the parsing went ok. If not (False), tell the user to enter again; else (True) the second param will be the converted value. Date, Double, Decimal etc all have a TryParse method.
This answer provides a more detailed explanation.
Many of the "primitive" data types have several parsing methods that can construct from a string representation.
Check the Parse and TryParse shared methods of Integer.