Random not working

Question

To clarify, multiple students objects and all of them are getting the same value.

I know this question has been asked before, but I have had no luck with the other posts about his topic. I have a random number generator ranging from 1-3. I then us %2 to make a bool value true or false. Every time I run the program I either get all true or all false. Here is my code. I know that random is not really random. What can I do to get more random numbers.

Random random = new Random();

public Student()
{
    int randomLevel=random.Next(1,3);
    level = (randomLevel % 2 == 0);
}

public bool readingLevel()//this always returns one value for the entire program.
{
    return level;
}

Answer 1

You are only assigning a random value to 'level' once during the constructor, so it will always have the initial value. Try:

public bool readingLevel()
{
     return (random.Next(1,3) % 2 == 0);
}

Edit:

Static Random random = new Random();
...

Answer 2

Some others have said this, but I think the point deserves underscoring with an example.

public class Student
{
    Random random = new Random(); 

    public Student() 
    { 
        int randomLevel=random.Next(1,3); 
        level = (randomLevel % 2 == 0); 
    } 

    public bool readingLevel()//this always returns one value for the entire program. 
    { 
        return level; 
    } 
}

public class Program
{
    public static void Main()
    {
        var students = new List<Student>();
        for (int i = 0; i < 10; i++)
            students.Add(new Student());

        //Now you have 10 Students; each Student has its own random number generator
        //The generators were created within microseconds of each other, so they most likely have THE SAME SEED
        //Because they have the same seed, they will generate identical sequences of numbers
        //Each student's reading level is calculated from the first call to .Next(1, 3) on its own RNG.
        //The RNGs have the same seed, so each will return the same value for the first call to .Next(1, 3)
        //Therefore, all students will have the same reading level!
    }
}

Answer 3

That is because you are using the random.Next() and the level evaluation within the constructor of your class, remember that the constructor is only executed when you create a new instance of your object, for having it executed several times create a different method where you call the random and the level evaluation, that way you'll get different values every time or use Something like this:

public bool Level()
{
     int randomLevel=random.Next(1,3); 
     level = (randomLevel % 2 == 0); 
     return level;
}

Answer 4

It looks like your random generator is an instance variable of the Student. Since the generator uses the current time as the seed, if you create a bunch of students within a short time, they will all have each have a generator with the same seed and the same results. You could make the random generator a static variable or, better yet, use constructor injection and pass the level into the Student's constructor.

class Student
{
  private static Random random = new Random();

  public Student()
  {
    level = random.NextDouble() < 0.5;
  }

  public bool readingLevel()
  {
    return level;
  }
}

or use constructor injection so your student class is deterministic.

class Student
{
  private boolean level;

  public Student(boolean readingLevel)
  {
    this.level = readingLevel;
  }
  public boolean readingLevel()
  {
    return level;
  }
}

Answer 5

public Student()
{
    int randomLevel=random.Next(1,3);
    level = (randomLevel % 2 == 0);
}

seems very much like a constructor for the Student class. In this constructor you are basically calculating a random number and storing it inside the level field. So if you use the same instance of Student throughout your entire program and call the readingLevel() method multiple times on this instance it will obviously return the same value -> the one that was done during the construction of this instance and that you stored in the level field.

So you might consider moving the random number generation logic into the readingLevel() method instead of simply returning the same value over and over again:

public class Student
{
    private Random random = new Random();

    public bool readingLevel()
    {
        int randomLevel = random.Next(1,3);
        return (randomLevel % 2 == 0);
    }
}

Now everytime you call this method on the same instance you should get a new calculation of a random number.

Answer 6

It looks like you're trying to get a random number!
Clippy

Well you can try something like this:

static Random random = new Random();

public Student()
{
    lock (random)
    {
        int randomLevel=random.Next(1,3);
        level = (randomLevel % 2 == 0);
    }
}
public bool readingLevel()//this always returns one value for the entire program.
{
    return level;
}

The problem with your snippet seems to be that you are instantiating a new Random class with each of your class instances. This is not the way Random is supposed to be used, but instead a single Random class instance should be used for acquiring multiple random numbers.

The Rationale for this is that Random in .Net uses a pseudo random algorithm based on state (a seed) that changes every time you ask for a new random number. By instantiating multiple random classes in a relatively short time span, there is a high chance that all of them will be initiated with the same seed (Based on system time) and all will give the same random number.

Answer 7

Try the following. Move the selection of the random level to the readingLevel function.

Random random = new Random(); 
public Student() 
{ 
}

public bool readingLevel()//this always returns one value for the entire program. 
{ 
  int randomLevel=random.Next(1,3); 
  level = (randomLevel % 2 == 0); 
  return level; 
} 

Answer 8

Well.

Consider what is happening here. When your Student is constructued, you get some random number, and then set it to the member variable level.

Then, at some other point, you call a function, readingLevel, which returns this previously set value.

Then, you may ponder to yourself: Exactly when would this function give a different value? Well, it will only do so when level gets a different value. And when does that happen? Well, it only happens in the constructor, so, that means, it never happens again for the life of the object ....

Answer 9

You are using random to simulate a true/false situation, so you are trying to limit the result to either 1 or 2. Given that you are doing an odd/even test on the result you might be better off doing:

int randomLevel = random.Next();
level = (randomLevel % 2 == 0);

Also If you create all your students in quick succession there's a good chance that your current code will return the same value for subsequent calls.

Answer 10

Create only one instance of Random and reuse it. Creating multiple instances of random in quick succession seeds to the same value and thus leads to the same sequence.

If your code in single threaded you can simply use a static property to hold the instance of Random.

The default seed value is derived from the system clock and has finite resolution. As a result, different Random objects that are created in close succession by a call to the default constructor will have identical default seed values and, therefore, will produce identical sets of random numbers. This problem can be avoided by using a single Random object to generate all random numbers. You can also work around it by modifying the seed value returned by the system clock and then explicitly providing this new seed value to the Random(Int32) constructor. For more information, see the Random(Int32) constructor.

http://msdn.microsoft.com/en-us/library/h343ddh9.aspx

Answer 11

Random random = new Random(DateTime.Now.Ticks);