I'm new to programming and I'm trying to build a die roller game in C#.
The program asks the user for the number of sides and then rolls a dice with a random number.
I have the following pseudocode:
ask user for the number of sides.
roll the die with a random number with max range being the number of sides.
tell the user the number rolled
My question is how do I roll the dice with generating a random number in range specified by the user?
The System.Random class is commonly used to generate casual random numbers.
It has an overload of a method called Next which generates a random integer that is greater than or equal to 0 and strictly less than the passed integer argument.
Thus if the user chooses an n-sided die, and you have an instance of Random r,
r.Next(n) + 1
will generate a random integer between 1 and n inclusive.
It is good practice to create a single instance of Random and reuse it, because if you create several instances close together they will all generate the same numbers.
Random random = new Random();
int randomNumber = random.Next(1, userInput);
One thing for you to know though is the random function isn't exactly random, its random but in the same random order everytime.. I'll let you look on your favourite search engine for seeding ;)
To get a Random integer between 0 and 100 with 100 not included:
Random random = new Random();
int randomNumber = random.Next(0, 100);
System.Random, specifically System.Random.Next(Int32, Int32) should get you started.
Random.Next(Int32, Int32)
Returns a random number within a specified range.
public int RollDice(int iNoSides)
{
var rand = new Random();
return rand.Next(iNoSides) + 1
}
A simple google of random number c# would of got you more or less this exact code.
EDIT
You have the link to the MSDN documentation from other answers and comments, I know your new to programming but the best way to learn is to try as hard as you can to get something. If you get to a state where your mind can't function any more, posting your attempt with your question on Stack will make people generally a lot happier that they are genuinely helping somebody that is stuck
EDIT 2
Following #Rawling's comment, I realised that the overload of the method states that Next(n) returns a Non-negative number less than the specified maximum.
Related
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I have this exercise:
Make a method that generates a random number between 1 and 100.
Ask the user to guess a number between 1 and 100.
Make a method that checks if the user's guess is equal to the random number that has been generated. This method will also say "higher" or "lower" until the user guesses the random number.
I have no problem with steps 1 and 2, but I'm having problems with the 3rd step. Here is my code so far:
static void Main(string[] args)
{
int randomNumber = GenerateRandomNumberMethod();
Console.WriteLine("Guess a number between 1 and 100:");
}
// generate random number method (step 2)
public static int GenerateRandomNumberMethod()
{
Random rdn = new Random();
int random = rd.Next(1,100);
return random;
}
//step 3 (Method to compare guessed number with random number)?
I hope it is not a stupid question, the answer is probably pretty simple.
Well, the first thing you want to do is to store the generated random number in a variable, so that it will not be re-generated after each time the user attempts.
The second thing you want to do is to create a method that will compare the user input against the randomly-generated number, and return a value indicating if the user input is smaller, equal, or higher than the generated number (A bool? might be a good choice for this).
The third thing you need is a safe way to convert the string the user entered to an int.
Do not make the common mistake of using Convert.ToInt32 - use int.TryParse instead. You do not want to throw an exception if the user entered Zohar instead of 123.
The fourth thing to do is to implement a loop - that will keep getting inputs from the user and tell them if the number is too high or too low. Exit the loop if the number is the same as the generated random number.
The last thing to do is to tell the user they finally guessed the correct number and exit (or maybe restart) the game.
Since it's clearly a homework assignment, I'll leave the coding part for you to handle, because you will not learn anything if you don't at least do it yourself, but at least now you have a plan.
Try
int userGuess = int.Parse(Console.ReadLine());
See this previous question on reading user input.
See this previous question on your exact problem.
See comments for note on int.Parse()
I am making a simple game in C# and using Random class to generate a random number every 2 seconds, but it gives numbers that I can guess in advance because it increments by a certain number each time.
private int RandomNumber;
//This Timer function runs every 2 seconds
private void TmrGenerateRandomNum(object sender, EventArgs e)
{
Random r = new Random();
RandomNumber = r.Next(50, 200); //Trying to get random values between 50 and 200
Label1.Text = RandomNumber.ToString();
}
This is literally the only code I have, and I am displaying the value each time through Label1. The problem is, for example, if I first get 52, the next "randomly"-generated value is 71 or 72, and the next one is 91 or 92, and the next one is 111 or 112. As you can see, it is incrementing by 20ish. Then it suddenly gets a real random value again like, say, 163. But then the next generated number is 183, again incremented by 20. Since 183+20 exceeds the range, it gets a real random value again, say 83. But the next number generated is again 103, or 104, and then 123 or 124...
This is not "Random" because you can tell around what number the next one is going to be... and this is driving me crazy.
Do you know why it does this, and is there a fix for this?
Random numbers use a seedvalue to start the sequence. If you give nothing, it takes to current datetime.now value. if you supply the same value (like 3842) you will get the same sequence of random values guaranteed. Your series seemed to be very closely related so you see the same values. All this can be read in the documentation on msdn, see Instantiate pseudo random :
Instantiating the random number generator
You instantiate the random number generator by providing a seed value (a starting value for the pseudo-random number generation algorithm) to a Random class constructor. You can supply the seed value either explicitly or implicitly:
The Random(Int32) constructor uses an explicit seed value that you supply.
The Random() constructor uses the system clock to provide a seed value. This is the most common way of instantiating the random number generator.
If the same seed is used for separate Random objects, they will generate the same series of random numbers. This can be useful for creating a test suite that processes random values, or for replaying games that derive their data from random numbers. However, note that Random objects in processes running under different versions of the .NET Framework may return different series of random numbers even if they're instantiated with identical seed values.
Source: https://msdn.microsoft.com/en-us/library/system.random(v=vs.110).aspx#Instantiate
You find more information and even methods to "better" cryptographical random methods linked above the source I cited.
While true random numbers are relatively difficult to generate, you should be able to get much better results than you are. The problem you're likely having right now, as suggested by comments, is that you should not be "starting over" every time the function is called. As a test, you can try passing some value like 5 as a parameter to the Random constructor. Then you will notice your results are really not random. To fix this, as the comments suggest, you should move the construction of the Random object somewhere global so that the randomness can "build" on itself over time instead of always being reset. Once you confirm that you can get different values with repeated calls, then remove the parameter to the Random constructor so that you don't get the same sequence of random numbers every time you restart your program.
More of an in-depth explanation:
Basically, it's pretty much impossible to generate truly random values in a computer, all of the random values you get are pseudo random and are based off of values like:
User input, like how many keys were pressed in the last 2 minuts
Memory usage, how many KB of memory is being used at this very moment
The most common one: Using the current time in mili seconds to generate a "seed" that's used to generate a series of numbers that are mathematical as randomized as possible
This is where the problem comes from. For example, if you were to have the following code
Random r1 = new Random();
Random r2 = new Random();
Console.WriteLine(r1.next())
Console.WriteLine(r2.next())
Miraculously, you will always get the same number from r1 and r2 despite them being two separate instances. It's because the code block is execute in a time window of <1 ms, which gives these two random number generators the same seed, thus they will generate the same list of numbers.
In your case, the number generator is instantiated every 2 seconds, thus they get an incrementing seed. It's hard to say if that will result in an incrementing starting number, but it might be a start.
So instead, try initializing a single Random() and always call the .next() function on it, and you should be getting a much more random list of numbers
The best you can do is use a CPRNG or Cryptograph Psudo Random Number Generator, it does not need to be seeded by tyhe user and in generally continnualy updates with system events.
To generate a cryptographically secure random number use the RNGCryptoServiceProvider class or derive a class from System.Security.Cryptography.RandomNumberGenerator.
See MSDN Random Class.
If I use two random numbers, how can I ensure that the first of these numbers generated is always larger than the second in order to present a subtraction or a divide quiz to the user?
You don't.
Just check which one is larger and present accordingly.
You generate the second random number and add it to the first one.
var max = 1000;
var rnd = new Random();
int a, b;
do
{
a = rnd.Next(max);
b = rnd.Next(max);
} while (a <= b);
You can use similar approach for more complex conditions too (for example if your task is to generate 2 numbers that in sum give more than 100, etc).
You will have to make your code smarter if probability of random numbers satisfying your condition is so small that generation takes too much time but for this particular task this approach is good enough.
You can generate numbers like this (pseudocode): (int)(a*rand()+b) where a and b control the range and starting point of your random numbers.
If a1=10, b1=1 for instance you get a range of 1-10. With a2=10 and b2=11 you get numbers in the range 11-20, which might be good for simple subtraction problems.
How should i be generating a random number between 0 and up to 2?
I am currently using a private static readonly Random object and call _random.Next(0, 2) BUT the values are not random ... I see sequences of 0,0,0,1,1,0,0,0,,1,1,1
The below is clearly not random. How should I be doing this?
Thanks a lot
If you mean you want random numbers 0 or 1, then what you’re doing is already correct.
If you want numbers 0, 1 or 2, then you need to write _random.Next(0, 3).
You are already doing it the right way (as long as your requirements for pseudo-random numbers doesn't include cryptographic security).
The problem is that randomness is statistically determined (using math), not intuitively determined (using your eyes).
For example, even if your random number sequence is uniformly random, given an infinite sequence of random numbers, you will still see one-hundred-thousand 1s in a row.
See this Wikipedia article on Pseudorandom Number Generators
If you are trying to get the numbers "0, 1, 2", then you may need to change your call to random.Next(0, 3). If you indeed only want 0 and 1, then leave it as it is.
Also, if you are creating instances of Random in multiple places in your code, you may get identical seeds, so will get identical sequences of random numbers. One way to avoid this would be to reuse the instance of the Random class between those two pieces of code, rather than creating new instances.
If you initialize Random with the same seed, you will get the same sequence of numbers. That's why it might be a good idea to use a time-based seed:
Random _random = new Random(DateTime.UtcNow.Millisecond);
Also, note that the upper bound in Next is exclusive. That means that Next(0, 2) will always return only 0 or 1 (but that might be what you wanted; somewhat unclear to me from the question).
The maxValue is "upto-and-not-included". If you wish to include 2, just write _random.Next(0,3)
I have been doing some testing on the Random class and I have used the following code:
while (x++ <= 5000000)
{
y = rnd.Next(1, 5000000);
if (!data.Contains(y))
data.Add(y);
else
{
Console.WriteLine("Cycle {2}: Repetation found for number {0} after {1} iteration", y, x, i);
break;
}
}
I kept changing the rnd max limit (i.e. 5000000) and I changed the number of iterations and I got the following result:
1) if y = rnd.Next(1, 5000) : The average is between 80 to 110 iterations
2) if y = rnd.Next(1, 5000000) : The average is between 2000 to 4000 iterations
3) if y = rnd.Next(1, int.MaxValue) : The average is between 40,000 to 80,000 iterations.
Why am I getting these averages, i.e. out of 10 times I checked for each value, 80% of the time I get within this average range. I dont think we can call it near to being Random.
What can I do to get a fairly random number.
You are not testing for cycles. You are testing for how long it takes to get a random number you've had before. That's completely different. Your figures are spot on for testing how long it takes to get a random number you had before. Look in wikipedia under "the birthday paradox" for a chart of the probability of getting a collision after a certain number of iterations.
Coincidentally, last week I wrote a blog article about this exact subject. It'll go live on March 22nd; see my blog then for details.
If what you want to test for is the cycle length of a pseudo-random number generator then you need to look for not a number you've had before, but rather, a lengthy exact sequence of numbers that you've had before. There are a number of interesting ways to do that, but it's probably easier for me to just tell you: the cycle length of Random is a few billion, so you are unlikely to be able to write a program that discovers that fact. You'd have to store a lot of numbers.
However, cycle length is not the only measure of quality of a pseudo-random number generator. Remember, PRNGs are not random, they are predictable, and therefore you have to think very carefully about what your metric for "randomness" is.
Give us more details: why do you care how "random" Random is? What application are you using it for that you care? What aspects of randomness are important to you?
You are assuming that the randomness is better if numbers are not repeated. That is not true.
Real randomness doesn't have a memory. When you pick the next number, the chance to get the same number again is just as high as any other number in the range.
If you roll a dice and get a six, then roll the dice again, there is no less chance to get a six again. If you happen to get two sixes in a row, that doesn't mean that the dice is broken.
The randomness in the Random class it of course not perfect, but that is not what your test reveals. It simply shows a phenomenon that you get with every random number generator, even if actually creates real random numbers and not just pseudo-random numbers.
You are judging randomness by repeat pairs, which isn't the best test for randomness. The repeats you see are akin to the birthday paradox: http://en.wikipedia.org/wiki/Birthday_problem, where a repeat event can occur with a small sample size if you are not looking for a specific event.
Per the documentation at http://msdn.microsoft.com/en-us/library/system.random.aspx
To generate a cryptographically secure
random number suitable for creating a
random password, for example, use a
class derived from
System.Security.Cryptography..::.RandomNumberGenerator
such as
System.Security.Cryptography..::.RNGCryptoServiceProvider.
A computer can't generate a real random number.
if You need a real random number (David gave you the best option from dot net framework)
you need an external random source.