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Generic math - .NET | Microsoft Learn[^]
The majority of types you'd want to perform mathematical operations on are structs. And you can't have an abstract base class for a struct. 
Also, as far as static members go, an abstract base class still wouldn't help; you can't "override" a static member from your base class.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Sometimes using an interface makes more sense than using abstract base classes (the good old "I am" or "I can" discussion). And some of these interfaces where of course defined in nuget packages.
This means to add a method or property, you would have to either rename the interface and support both for a while, or you would force anyone who use your nuget package to reimplement the interface. Doable when users only have only a few nuget packages, and the runtime will guard you against a newer version of a package than you expect.
However with the way a lot of software is structured today it does not work anymore. Projects use a lot of nuget packages, and they have internal dependencies meaning updating one nuget package could lead to a chain reaction of having to update others... and sometimes there just was not a way of getting all of them compatible. Basically DLL hell was replaced... by NuGet hell.
Allowing interfaces to add methods/properties and remain backwards compatible makes it easier to write code that will survive when running with newer version of one or another 4th level dependent nuget package than it was written against.
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I am following the online C# tutorials here: create class and objects.
I cannot get the code to envoke the class to create an object. I have some Python knowledge but am learning C#. I am using VS 2022 community edition and running on Windows 10.
I will post the code below but what happens is the Console.WriteLine("Hello, World!"); executes but not the attempt to envoke the class.
I am guessing the code should work like this:
1. C# executable looks for
static void Main(string[] args)
2. Within this main module is the statement:
Person person = new Person();
This line should create an object person.
3. The following lines should assign values to the person object's attributes
person.Name = "Daniel";
person.Age = 28;
person.Haspet = true;
4. The line :
person.Greeting();
should cause the class to be called:
public void Greeting()
{
Console.WriteLine("Within Greeting method. Name is:" + Name +" age is:"+ Age);
Console.ReadLine();
}
but this code does not execute. What am I am getting wrong?
Code:
Console.WriteLine("Hello, World!");
namespace crltemp
{
public class Person
{
public string Name;
public int Age;
public bool Haspet;
public void Greeting()
{
Console.WriteLine("Within Greeting method. Name is:" + Name + " age is:" + Age);
Console.ReadLine();
}
}
class Program
{
static void Main(string[] args)
{
Person person = new Person();
person.Name = "Daniel";
person.Age = 28;
person.Haspet = true;
person.Greeting();
}
}
}
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Quote:
Console.WriteLine("Hello, World!");
namespace crltemp
{
...
You've created a project using the new Top-level statements[^] syntax, and forgotten to remove the boilerplate.
As a result, the compiler will generate an entry-point for you which will simply write "Hello, World!" to the console and then exit. The additional Main method in your Program class will never be called.
Remove the code outside of your namespace, and your code should start behaving as expected.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Thanks for your very swift reply to a very basic question. Removing the top-level statement meant the compiled program ran as intended. 
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Yet another example of Hutber's Law.
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"Hutber's Law". No idea what that meant. Looked it up. Still no idea what it means. I think I've been insulted but I don't know. Play nice.
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My reply was for Richard Deeming, rather than you. But I was alluding to the fact that Microsoft has changed the templates so you don't need to put the main method in a C# Console app, which confuses people because most of the tutorials that you can find will have been created before this "feature" was introduced. And for the record (not an insult to you) Hutber's law - Wikipedia[^].
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They should never have added that "feature" ... 
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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I have to extract payment data from PDD's. Some have just one or two lines I need, and other have rows and columns of data.
What's the best way to extract this data using C#?
In theory, theory and practice are the same. But in practice, they never are.”
If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
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Kevin, you've been here long enough; asked enough questions already to know that that's far too vague a query to get anything practical in terms of an answer - all we can do is generically direct you to something like NuGet Gallery | iTextSharp 5.5.13.3[^] and suggest you start there!
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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I was hoping for "I've used...." or "Try this api" kind of answers. I don't have enough info to give more detail because I don't know where to start
In theory, theory and practice are the same. But in practice, they never are.”
If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
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Most people don't use PDFs to transfer data between applications of any kind, so the pool of people who could answer that question is exceedingly small, like none of the regulars around here would have done it.
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If it's a pdf of an image, there's no text either.
There is no "general" solution.
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
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I know what you mean, but ... as Dave says PDF is not a data transfer format, it's a user presentation format.
Using it to transfer computer readable info is like using Word to send a bitmap in an email - you could probably do it, but anyone who saw what you were doing would be wondering "what fool came up with *that* idea?" 
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Ya I hear ya. My client has Invices in PDF format that need data extracted. I found https://docs.apryse.com/which looks promising.
In theory, theory and practice are the same. But in practice, they never are.”
If it's not broken, fix it until it is.
Everything makes sense in someone's mind.
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I guess it depends on where the PDF's originate: if it's a single company and they will guarantee to never, ever, ever change the format in writing signed in blood I might give it consideration - but invoices? I can see so many ways in which that could go seriously wrong and somebody end up in jail for tax evasion ... I'd probably decline to quote on that job myself.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Yes. Should be using EDI ... or "something".
EDI 810 Invoice: Transactions, Format & Specifications | Astera
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
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In some businesses (especially insurance), it was common to use PDFs for data capture purposes. This would then be transferred over to companies to process this and convert the data contained inside into something that could be used in the office.
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Yes, if I remember correctly PDF has a Forms mode which limits what users can enter and where?
But you wouldn't use that for invoices! 
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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I've seen this used for something akin to invoices in the past. That's how the commercial insurance industry operates; they do love their PDFs.
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I've used Ghostscript to parse PDF files before. You don't even need to write any code, just use the precompiled tools.
ghostscript extract PDF text
They have a C# wrapper but I've never used it.
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Tika has a PDF parser. Among many others.
Apache Tika – Apache Tika[^]
You would of course still need to code to each individual different format.
(Note that there are even image parsers.)
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The title os this message might look like a joke, but it is actually very serious.
The other day I wanted to implement my own BigInteger class, and I was using bytes as the backing fields. Yet, I would only use values from 0 to 9 for each digit.
Bing AI suggested me to create an enum with values ranging from D0 to D9 (I think their actual values are obvious).
Yet, using an enum like that doesn't forbid users from doing things like (DecimalDigit)56 and pass 56 to an enum that was only supposed to support values ranging from 0 to 9.
Of course I can validate the values at run-time... but the entire purpose of using an enum was to avoid mistakes like that.
So, my solution was to create a class (in fact, a struct, but a class serves the same purpose) that has a private constructor, and has public static readonly fields ranging from D0 to D9. This way, users outside of the class, except if they really want to mess up (like using unsafe reflection) cannot pass values that aren't in the 0-9 range.
This also reminded me of a job where we had one enum with like 20 values... and then, many, many, many switches to get the many different traits of those enums.
Wouldn't it be better to just have classes, with all the traits, and use the classes?
Aside from the use of the enum in switch statements, they work the same in most cases, work even easier in cases where we usually had to use helper methods... and if a new trait is added, we have a single place (where the enum values are declared) to fix... with no chance of "forgetting" a case in a switch somewhere else.
What do you guys think?
Example:
public struct DecimalDigit
{
public static readonly DecimalDigit D0 = new(0);
public static readonly DecimalDigit D1 = new(1);
public static readonly DecimalDigit D2 = new(2);
public static readonly DecimalDigit D3 = new(3);
public static readonly DecimalDigit D4 = new(4);
public static readonly DecimalDigit D5 = new(5);
public static readonly DecimalDigit D6 = new(6);
public static readonly DecimalDigit D7 = new(7);
public static readonly DecimalDigit D8 = new(8);
public static readonly DecimalDigit D9 = new(9);
private DecimalDigit(byte value)
{
_value = value;
}
private readonly byte _value;
public byte ByteValue
{
get => _value;
}
}
public enum DecimalDigit:
byte
{
D0,
D1,
D2,
D3,
D4,
D5,
D6,
D7,
D8,
D9
}
Notice that although the enum version is smaller, if we need to add names for the values, in the class we just add a property, for the real enum, we create a helper method.
If we need to convert them to numbers, add an emoji or whatever, in the first version it is just a matter of adapting the class, while in the second it is a matter of creating more (and somewhat unrelated) methods.
Edit: I had some questions about why create a new decimal class. There is not a real need to create one. I just wanted to do it as an exercise. I can tell that .NET implemented BigInteger is way faster than my class. Yet, just by writing the UnsignedDecimalInteger I saw opportunities to write Quadbits (effectively, half of a hexadecimal value... or just 4 bits), so in one byte I can store 2 Quadbits. I also saw opportunities for caching of the internal buffers I use... and I am just "relearning" how to do math the "old way" using decimal values. I will, at some point, improve it to use 32 or 64 bits at once.
Also, one of the next steps, be it with BigInteger or my UnsigedDecimalInteger, is to create a BigDecimal or similar class. In fact, having a value alone (without caring about operations), I just need to have a value telling where the dot separating the integer part and the fractional part. Or, I can literally have two BigInteger (or similar), one for the left side, and one for the right side, of the decimal.
modified 1-Aug-23 18:09pm.
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I use .IsDigit more often than defining what one is. Enums make code more readable. And can save storage.
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
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