C#•2mo ago

rgument 2: cannot convert from 'int' to 'System.Func<int, decimal>'

C#
int lineReading;

if (inputStudentFile == "1")
{
    inputStudentFile = "studenten-1.txt";
    using (FileStream file = new FileStream(inputStudentFile, FileMode.Open, FileAccess.Read))
    {
        using (StreamReader reader = new StreamReader(file))
        {
            while (!reader.EndOfStream)
            {
                lineReading =         Convert.ToInt32(reader.ReadLine());
                nums.Add(lineReading);
                Console.WriteLine(lineReading);
            }
            if (inputMenu == "1")
            {
                nums.Sum(lineReading);
            }
        }
    }
}

C#
int lineReading;

if (inputStudentFile == "1")
{
    inputStudentFile = "studenten-1.txt";
    using (FileStream file = new FileStream(inputStudentFile, FileMode.Open, FileAccess.Read))
    {
        using (StreamReader reader = new StreamReader(file))
        {
            while (!reader.EndOfStream)
            {
                lineReading =         Convert.ToInt32(reader.ReadLine());
                nums.Add(lineReading);
                Console.WriteLine(lineReading);
            }
            if (inputMenu == "1")
            {
                nums.Sum(lineReading);
            }
        }
    }
}

Error (the title) is when I do nums.Sum(lineReading); idk why

31 Replies

Kimo_TerapyOP•2mo ago

in short, the user has a "menu" where they can choose which .txt file to open. Then they get the option what to do with it. When they press "1" it will read the file, and add up all the numbers inside of that file and then do the sum with the numbers it has every number is seperated on each line in the files to make it easier to read. Thats why there is no Split()

mtreit•2mo ago

Why are you passing an argument to Sum() ?

viceroypenguin•2mo ago

nums.Sum() takes a lambda, not a value you're tyring to do [1, 2, 3].Sum(4), which is non-sensical.

mtreit•2mo ago

You need to assign the value of nums.Sum() (no argument) to a variable.

viceroypenguin•2mo ago

also, nums.Sum() does not change anything, it returns the sum calculated. so unless you print it (Console.WriteLine()) or store it (var x = ), it's useless

Kimo_TerapyOP•2mo ago

oh yea pffft 🤦‍♂️ sorry i been making exercises for a few hours now

mtreit•2mo ago

result = nums.Sum()`

result = nums.Sum()`

Kimo_TerapyOP•2mo ago

yea this is only a snippet of the code for the rest does it look ok

viceroypenguin•2mo ago

it looks like it works. it's not how i would write it, but i'm not one to judge...

Kimo_TerapyOP•2mo ago

still learning bro 😭

mtreit•2mo ago

inb4 someone says don't use Convert.ToInt32

viceroypenguin•2mo ago

i'd do something like:

var result = File.ReadAllLines(inputStudentFile)
  .Select(l => int.TryParse(l, out var val) ? val : 0)
  .Sum();

var result = File.ReadAllLines(inputStudentFile)
  .Select(l => int.TryParse(l, out var val) ? val : 0)
  .Sum();

Kimo_TerapyOP•2mo ago

looks clean but looks like chinese to me 😭

mtreit•2mo ago

BTW if you want to use StreamReader you can pass it the file name directly in the constructor. You don't need to first open a raw FileStream and then pass that in. So you can simplify that code a bit.

Kimo_TerapyOP•2mo ago

wait whaaaaat

viceroypenguin•2mo ago

also, yo udon't have to use {} with using

using var streamReader = new StreamReader(inputStudentFile);
while (!reader.EndOfStream)
{
}

using var streamReader = new StreamReader(inputStudentFile);
while (!reader.EndOfStream)
{
}

but File.ReadAllLines() gives you an array with every line of the file, so yo udon't even hve to mess with readers or while loops

Kimo_TerapyOP•2mo ago

damn... then why they teaching it to us like this 😭

mtreit•2mo ago

Learning how to use streaming APIs is useful because sometimes you don't want to read the entire thing into memory. For instance if the file is gigabytes in size.

viceroypenguin•2mo ago

var lines = File.ReadAllLines(inputStudentFile);
var numbers = new List<int>(lines.Length);
foreach (var line in lines)
  numbers.Add(int.Parse(line));
var result = numbers.Sum();

var lines = File.ReadAllLines(inputStudentFile);
var numbers = new List<int>(lines.Length);
foreach (var line in lines)
  numbers.Add(int.Parse(line));
var result = numbers.Sum();

Kimo_TerapyOP•2mo ago

oh ok

viceroypenguin•2mo ago

then this can be shortened to the version i gave you above by learning about LINQ and .Select()

mtreit•2mo ago

Another small thing you can fix if you want. The idiomatic way to stream through an entire text file is:

while (sr.ReadLine() is string line)
{
}

while (sr.ReadLine() is string line)
{
}

That way you get the line in one shot and don't need to use EndOfStream.

viceroypenguin•2mo ago

yup. useful to knwo both streamreader and readalllines.

Kimo_TerapyOP•2mo ago

so here sr.ReadLine(); assigns it to the variable line (if its a valid string of course)

viceroypenguin•2mo ago

and if it's not null

mtreit•2mo ago

Yes, this is using a very neat feature of C# called pattern matching. When you pattern match on the result of a method call (using is in this case) you can assign it to a variable at the same time (in this case line) if it matches the pattern. It's very nice for this kind of thing.

Kimo_TerapyOP•2mo ago

yea super chill

mtreit•2mo ago

If you want to learn more about pattern matching, @viceroypumpkin | 🦋🎃 did a very nice talk on it 🙂 https://youtu.be/w3m-THz--6A

.NET Foundation

YouTube

Solution2: Adventures in Pattern Matching with Stuart Turner

An in-depth guide to migrating existing code to use pattern matching! Join us on Discord: https://discord.com/invite/csharp JetBrains: https://www.jetbrains.com/ O'Reilly: https://www.oreilly.com

Kimo_TerapyOP•2mo ago

appreciate it thats u in the vid? @viceroypumpkin | 🦋🎃

viceroypenguin•2mo ago

aye, yes

Kimo_TerapyOP•2mo ago

nice hat

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rgument 2: cannot convert from 'int' to 'System.Func<int, decimal>'

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