C#•2y ago

❔ Indexing with [] to an expression type IEnumerable / array

Hi, I am trying to do some c# challanges as a way to begin my c# journey, but I am currently stuck on this. To elaborate, I am trying to fill each of the spaces in the array with (num1 * i), but I cannot. So far, I have been stuck for almost an hour while trying to do different things. I think, the main problem is that I have not created a space for the values to reside in the array, though I thought putting (length) in would solve that (spoiler, it did not)

74 Replies

Angius•2y ago

IEnumerable allows you only to enumerate the collection It does not allow for random access, so indexing into it You're creating a list, so... store it as a list

9.h•2y ago

I see, the challenge provided resource which used IEnumerable, thus I thought I should too I will try using list, then

Angius•2y ago

You can, but you'd have to foreach over the collection instead, or while over it Using a list where you create a list is much simpler

9.h•2y ago

I will try doing that later, but first I want to get it to work using list

9.h•2y ago

Is this progress?

Angius•2y ago

You initialized the list to a given size, but it doesn't have any elements There's no ith element

9.h•2y ago

I assumed that by adding size length to it, it would create the length amount of spaces I could put items into How can I create the i th element? There has to be enough elements in the list to fit all i's up to length

Angius•2y ago

Ah, wait, I see what the issue might be

MODiX•2y ago

Angius#1586

REPL Result: Success

var l = new List<int>(3);
for (var i = 0; i < l.Count; i++)
    l[i] = 7;
l

var l = new List<int>(3);
for (var i = 0; i < l.Count; i++)
    l[i] = 7;
l

Result: List<int>

[]

[]

Compile: 535.335ms | Execution: 53.964ms | React with ❌ to remove this embed.

Angius•2y ago

This works... kinda

MODiX•2y ago

Angius#1586

REPL Result: Failure

var l = new List<int>(3);
for (var i = 0; i < 3; i++)
    l[i] = 7;
l

var l = new List<int>(3);
for (var i = 0; i < 3; i++)
    l[i] = 7;
l

Exception: ArgumentOutOfRangeException

- Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')

- Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')

Compile: 536.939ms | Execution: 50.378ms | React with ❌ to remove this embed.

Angius•2y ago

While this throws Yeah, because the count of the list is still 0

9.h•2y ago

where does l.Count come from in this case

MODiX•2y ago

Angius#1586

REPL Result: Success

new List<int>(300).Count

new List<int>(300).Count

Result: int

Compile: 447.376ms | Execution: 25.035ms | React with ❌ to remove this embed.

9.h•2y ago

l doesn't exist prior to that line

Angius•2y ago

List has a property Count

9.h•2y ago

Oh by l did you mean List? So List.Count

Angius•2y ago

Yes l is the list

9.h•2y ago

oh shid ooga booga I'm smart Okay I shall try that

Angius•2y ago

So, one of two ways I'd go about it Either use an array instead of a list

9.h•2y ago

Btw when you use var, do you use it for simplicity sake as var can be anything or should I use var instead of int too?

Angius•2y ago

Or use the fact that a list is resizeable I use it everywhere tbh No reason not to And var x = 8; and int x = 8; are the exact same thing anyway

9.h•2y ago

Do you have to make the list a variable? in this case var l Can you just do List.Count instead nonoonno Wait I am stupid I understand

Angius•2y ago

Which list would List.Count refer to?

9.h•2y ago

Exactly I realized that when I looked at it again Thank you I'll try that

9.h•2y ago

This does not work by the way? Unless I did something wrong which is likely

Angius•2y ago

Odd, what's the error?

9.h•2y ago

Oh yeah I should mention I am using the .net framework and stuff I don't know if that is relevant but

Angius•2y ago

Ah, the old one?

9.h•2y ago

Wait lol it fixed itself lmao

Angius•2y ago

Might matter, dunno

9.h•2y ago

I let it stay like that for a minute while waiting for an answer and it stopped displaying as an error

Angius•2y ago

VS gonna VS I guess ¯\_(ツ)_/¯ Any particular reason you're using some old version of the framework to learn? And what version is it, exactly?

9.h•2y ago

This one to be exact

9.h•2y ago

Does what you said still apply

Angius•2y ago

Yeah .NET Framework is old and ass, but it works mostly well

9.h•2y ago

Okay, so mainly my college using this one and basically everything I try works so why change it?

Angius•2y ago

Well, depending on the version 4.8 is decent, 2.0 is hell And so on

9.h•2y ago

How can I check my version?

Angius•2y ago

In the csproj file Or right-click on your project in the solution explorer and open the properties

9.h•2y ago

I cannot find the version in the csproj file I'll try the other thing Oh no no nvm I found it 4.7.2

Angius•2y ago

Not horrible Not that much changed since then, so what I say should apply

9.h•2y ago

I am still a beginner plus this is what my college is using so I'd rather use it unless it will severely hinder my development

Angius•2y ago

Yeah, it's fine if your college uses it

9.h•2y ago

Angius•2y ago

As long as you're aware it's outdated and we got many a cool feature since then Yep, that's how complex objects get printed You get their name

9.h•2y ago

How can I display the array in a tangible form so I can confirm whether or not my code works as intended?

MODiX•2y ago

Angius#1586

REPL Result: Success

class Person{};
var p = new Person();
Console.Write(p);

class Person{};
var p = new Person();
Console.Write(p);

Console Output

Submission#0+Person

Submission#0+Person

Compile: 601.349ms | Execution: 73.677ms | React with ❌ to remove this embed.

Angius•2y ago

Could use string.Join() for example To join all the elements with a comma or something

9.h•2y ago

intellisense is a blessing But it did not work hm I put this before the console writeline string.Join(",", l.ToArray());

MODiX•2y ago

Angius#1586

REPL Result: Success

var list = new List<int>(){1, 2, 3, 4, 5, 6};
Console.Write(string.Join(", ", list));

var list = new List<int>(){1, 2, 3, 4, 5, 6};
Console.Write(string.Join(", ", list));

Console Output

1, 2, 3, 4, 5, 6

1, 2, 3, 4, 5, 6

Compile: 589.822ms | Execution: 81.709ms | React with ❌ to remove this embed.

Angius•2y ago

It does work Your list might be empty

9.h•2y ago

Likely to be the case I fixed it and it does not display anything so yeah

Angius•2y ago

Aight, show your current code, let's see

9.h•2y ago

Should I just take a ss or do the fancy code thing

Angius•2y ago

Post the fancy code $codegif

MODiX•2y ago

https://cdn.discordapp.com/attachments/364492811489509376/892176158312001586/code.gif

9.h•2y ago

            Console.WriteLine("Enter the number:");
            int num1 = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Enter the length:");
            int length = Convert.ToInt32(Console.ReadLine());
            var l = new List<int>(length);
            for(int i = 0; i < l.Count; i++)
            {
                l[i] = num1 * i;
            }
            Console.WriteLine(string.Join(", ", l));
            Console.ReadLine();

            Console.WriteLine("Enter the number:");
            int num1 = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Enter the length:");
            int length = Convert.ToInt32(Console.ReadLine());
            var l = new List<int>(length);
            for(int i = 0; i < l.Count; i++)
            {
                l[i] = num1 * i;
            }
            Console.WriteLine(string.Join(", ", l));
            Console.ReadLine();

oop

Angius•2y ago

Well, the list will have a count of 0 It has a size of length, but there aren't any elements there

9.h•2y ago

also another problem is that the first element will be 0 since i is 0

Angius•2y ago

Sure is

9.h•2y ago

any num * 0 = 0 Add() wouldn't work would it?

Angius•2y ago

The issue is that Count is 0, so no, it would not You can solve it two ways: 1. Use the length you got, not the list's .Count for your loop, then use .Add() 2. Use an array instead of a list

reflectronic•2y ago

new List<int>(length); is going to do the exact same thing as new List<int>();. it's not what you want here

9.h•2y ago

9.h•2y ago

the first one works I'ma try using an array too to get familiar with it Thanks for all the help btw

Henkypenky•2y ago

in case no one mentioned, don't forget the potential problems with Convert.ToInt32 TryParse is a much safer choice

9.h•2y ago

Such as? If I want to include numbers in an array/list, what else should I do other than Convert.ToInt32? In my college the teacher taught me to do that whenever trying to get an int from the user

Henkypenky•2y ago

$tryparse

MODiX•2y ago

The TryParse pattern is considered best practice of parsing data from a string: - a TryParse method returns true or false to inform you if it succeeded or not, so you can use it directly in a condition, - since C# 7 you can declare a variable that will be used as an out argument inline in an argument list, - it forces you to check if the out argument contains valid data afterwards, Avoid: Convert.ToInt32 — it's a bad choice for parsing an int. It exists only for backwards compatibility reasons and should be considered last resort.

return Convert.ToInt32(null); //returns 0. null should not be considered as 0 ever
return Convert.ToInt32("asdf"); //throws FormatException

return Convert.ToInt32(null); //returns 0. null should not be considered as 0 ever
return Convert.ToInt32("asdf"); //throws FormatException

(Note: Convert does contain useful conversion methods: To/FromBase64String, To/FromHexString, ToString(X value, int toBase), ToX(string? value, int fromBase)) Avoid: int.Parse — you have to use a try/catch statement to handle invalid input, which is a less clean solution.

var number = int.Parse("abc"); //throws FormatException
var number = int.Parse(""); //throws FormatException

var number = int.Parse("abc"); //throws FormatException
var number = int.Parse(""); //throws FormatException

Use int.TryParse https://docs.microsoft.com/en-us/dotnet/api/system.int32.tryparse?view=net-5.0#System_Int32_TryParse_System_String_System_Int32__

if (int.TryParse(someInput, out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

if (int.TryParse(someInput, out var result))
{
  Console.WriteLine($"Thanks for giving me the following number: {result}!");
}
else
{
  Console.WriteLine("You didn't give me a valid number :c");
}

Int32.TryParse Method (System)

Converts the string representation of a number to its 32-bit signed integer equivalent. A return value indicates whether the operation succeeded.

9.h•2y ago

I am a bit confused as to what parsing is, and google's answer is not the most helpful Basically is parsing changing a string into a value

Henkypenky•2y ago

not only strings, but yes, basically with TryParse you don't need to manage exceptions and can check the result of said parse

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Indexing with [] to an expression type IEnumerable / array