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;
        }
    }
}

Please specify only the code's purpose, not a specific request, in the title. — Jamal
– Jamal, Commented May 18, 2015 at 13:48

Dion V. · Accepted Answer · 2015-05-18 13:53:21Z

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 :)

answered May 18, 2015 at 13:53

Dion V.

5291 gold badge4 silver badges10 bronze badges

\$\begingroup\$ I got an error with the next one ... return werknemers.Where(w => werknemerId == w.Id).FirstOrDefault().AantalEenheden; throw new KeyNotFoundException(); \$\endgroup\$

Awa
– Awa

2015-05-18 14:18:34 +00:00
Commented May 18, 2015 at 14:18
\$\begingroup\$ @Awa it helps if you tell us what error it is :) \$\endgroup\$

Dion V.
– Dion V.

2015-05-18 14:32:14 +00:00
Commented May 18, 2015 at 14:32
\$\begingroup\$ Object reference not set to an instance of an object \$\endgroup\$

Awa
– Awa

2015-05-18 14:47:38 +00:00
Commented May 18, 2015 at 14:47
\$\begingroup\$ @Awa I was hoping you'd figure that out by yourself, therefore I am leaving it for exercise. A big hint: FirstOrDefault(). \$\endgroup\$

Dion V.
– Dion V.

2015-05-18 14:49:22 +00:00
Commented May 18, 2015 at 14:49

Add a comment |

ratchet freak · Accepted Answer · 2015-05-18 13:51:31Z

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();
}

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