C# Console Program Indexer only finds the FIRST item in my List<>

Question

Below is a very basic program with three classes which makes use of an Indexer to search for a person within a List<> per based on their age.

Person.cs Below:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Indexer1
{
    public class Person
    {
        private string name;
        private string surname;
        private int age;

        public int Age
        {
            get { return age; }
            set { age = value; }
        }


        public string Surname
        {
            get { return surname; }
            set { surname = value; }
        }


        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        public override string ToString()
        {
            return string.Format("{0} {1} {2}", name, surname, age);
        }

        public Person(string name, string surname, int age)
        {
            this.name = name;
            this.surname = surname;
            this.age = age;

        }
    }
}

Indexer.cs instantiates Person in List<> per Below:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Indexer1
{
    public class Indexer
    {
        List<Person> per = new List<Person>();

        public Indexer()
        {
            per.Add(new Person("Joe", "Soap", 25));
            per.Add(new Person("Marry", "Jane", 82));
            per.Add(new Person("Garry", "Zuma", 37));
            per.Add(new Person("Nelson", "Mabaso", 14));
        }

        public Person this[int indexes]
        {
            get
            {
                foreach (Person item in per)
                {
                    if (item.Age == indexes)
                    {
                        return item;
                    }
                    else
                    {
                        return null;
                    }
                }
                return null;
            }
            set
            {
                per[indexes] = value;
            }
        }
    }
}

Program.cs instantiates the indexer to allow for search and find, Below:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Indexer1
{
    class Program
    {
        static void Main(string[] args)
        {
            Indexer ind = new Indexer();

            Console.WriteLine("enter in age of person you are searching for");
            int age = int.Parse(Console.ReadLine());

            Console.WriteLine();
            Console.WriteLine("{0} {1} {2}", ind[age].Name, ind[age].Surname, ind[age].Age);

            Console.ReadKey();
        }
    }
}

When I run the program and search for the first person added to the List<> per "Joe Soap" by entering in his age: 25 when prompted, I am able to find him successfully and display all his info.

But as soon as I search for anyone else in the List<> per, let's say "Garry Zuma" by entering in his age: 37 when prompted, the program fails and throws an exception:

An unhandled exception of type 'System.NullReferenceException' occurred in Indexer1.exe Additional information: Object reference not set to an instance of an object.

I have tried searching on that exception but I couldn't find anything that solved my problem.

Your guys help and assistance is much appreciated.

Run your program in the debugger and go through step by step to see what your program is doing. — chris, May 18 '16 at 22:48
Aside from anything else, now would be a good time to learn about automatically implemented properties. — Jon Skeet, May 18 '16 at 22:51
To expand, `private int age; public int Age { get { return age; } set { age = value; } }` can simply be `public int Age {get; private set;}`. Hopefully that provides some incentive to learn about them. — chris, May 18 '16 at 22:52
Hi guys, I probably should have mentioned that I am a newby to c#. Looking at it now, it is a VERRRRRY simple problem that I had. But I appreciate the advise very much! :-) — FireHawk2300, May 18 '16 at 22:58
@chris : But private variable != private set. Shouldn't it just be `public int Age {get; set;}`? — Visual Vincent, May 18 '16 at 23:11
@VisualVincent, Yes, oops. I didn't look hard enough to see the public setter. — chris, May 18 '16 at 23:13

score 3 · Accepted Answer · edited May 19 '16 at 16:54

3

You need to remove the following code from the indexer

else
{
   return null;
}

That code prevents the loop ever getting past the first item in the list

edited May 19 '16 at 16:54

sujith karivelil

28,671
6
55
88

answered May 18 '16 at 22:50

Alastair Brown

1,598
8
12

I have formatted the code in this answer, please properly format the post for the next time. thank you – sujith karivelil May 19 '16 at 16:55

score 2 · Answer 2 · answered May 18 '16 at 22:49

Take a look into the iteration process. Consider that In the first iteration, if (item.Age == indexes) is evaluates to false then the method will return null to the calling method( Rest of iterations ware skipped). So what you need to do is, Remove the else{..} part; SO that The method will return Person object if it satisfies the condition or else will return null after the iteration.

public Person this[int indexes]
{
    get
    {
        bool isFound = false;
        foreach (Person item in per)
        {
            if (item.Age == indexes)
            {
                return item;
            }                   
        }
        return null;
    }
    set
    {
        per[indexes] = value;
    }
}

C# Console Program Indexer only finds the FIRST item in my List<>

2 Answers2