How to use 1 for loop in a method in stead of using the same for loop over and over again

Question

Since i'm still learning C# i've made an exercise but it seems like i'm using the same code over and over again. I do realize I have to use a helper method to get rid of the 'useless' code.

How can I put my for loops into a helper method ?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace NewTryoutExamen
{
 class Ploeg
 {
 private List<Werknemer> werknemers = new List<Werknemer>();
 public void VoegWerknemerToe(Werknemer w)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (w.Id == werknemers[i].Id)
 throw new DuplicateWaitObjectException();
 }
 werknemers.Add(w);
 }
 public uint Prestatie(uint werknemerId, uint hoeveelheid)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (werknemerId == werknemers[i].Id)
 return werknemers[i].VoegVerkopenToe(hoeveelheid);
 }
 throw new KeyNotFoundException();
 }
 public uint GeefAantalEenheden(uint werknemerId)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (werknemerId == werknemers[i].Id)
 return werknemers[i].AantalEenheden;
 }
 throw new KeyNotFoundException();
 }
 public double GeefTotaalLoon(uint werknemerId)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (werknemerId == werknemers[i].Id)
 return werknemers[i].TotaalLoon();
 }
 throw new KeyNotFoundException();
 }
 public Werknemer ToonWerknemerDetails(uint werknemerId)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (werknemerId == werknemers[i].Id)
 return werknemers[i];
 }
 throw new KeyNotFoundException(); 
 }
 public double Basisloon(uint werknemerId)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (werknemerId == werknemers[i].Id)
 {
 return werknemers[i].Basisloon;
 }
 }
 throw new KeyNotFoundException();
 }
 public double Commissie(uint werknemerId)
 {
 for (int i = 0; i < werknemers.Count; i++)
 {
 if (werknemerId == werknemers[i].Id)
 {
 return werknemers[i].Commissie;
 }
 }
 throw new KeyNotFoundException();
 }
 public override string ToString()
 {
 string res = "";
 string Id;
 for (int i = 0; i < werknemers.Count; i++)
 {
 Id = string.Format("{0:0000}", werknemers[i].Id);
 res += Id + " - " + werknemers[i].Naam + " " + werknemers[i].Voornaam + " ( eenheden: " + werknemers[i].AantalEenheden + ")" + Environment.NewLine;
 }
 return res;
 }
 }
}

• Jamal: Please specify only the code's purpose, not a specific request, in the title.

Answer 1

You should definitely look into LINQ. It saves alot of space.

A few reworks;

for (int i = 0; i < werknemers.Count; i++)
{
 if (w.Id == werknemers[i].Id)
 throw new DuplicateWaitObjectException();
}

becomes

if(werknemers.Any(wn => w.Id == wn.Id)
{
 throw new DuplicateWaitObjectException();
}

And

for (int i = 0; i < werknemers.Count; i++)
{
 if (werknemerId == werknemers[i].Id)
 return werknemers[i].VoegVerkopenToe(hoeveelheid);
}

becomes

return werknemers.Where(w => w.Id == werknemerId).FirstOrDefault().VoegVerkopenToe(hoeveelheid);

I'll leave the rest as an excercise :)

• Awa: I got an error with the next one ... return werknemers.Where(w => werknemerId == w.Id).FirstOrDefault().AantalEenheden; throw new KeyNotFoundException()
• Dion V.: @Awa it helps if you tell us what error it is :)
• Awa: Object reference not set to an instance of an object
• Dion V.: @Awa I was hoping you'd figure that out by yourself, therefore I am leaving it for exercise. A big hint: FirstOrDefault().

Answer 2

There is a pre-built method for testing if any element matches a condition:

if(werknemers.Any(werknemer => w.Id == werknemer.Id)){
 throw new DuplicateWaitObjectException();
}
werknemers.Add(w);

However you look up every werknemer a lot based on the ID. You should use a Dictionary<uint, Werknemer> instead which includes methods to check if a key is already used and a way to get the object back with the key:

public double Commissie(uint werknemerId)
{
 if(werknemers.ContainsKey(werknemerId))
 return werknemers[werknemerId].Commissie;
 }
 throw new KeyNotFoundException();
}