How to generate a random 10 digit number in C#?

Question

I'm using C# and I need to generate a random 10 digit number. So far, I've only had luck finding examples indicating min maximum value. How would i go about generating a random number that is 10 digits, which can begin with 0, (initially, I was hoping for random.Next(1000000000,9999999999) but I doubt this is what I want).

My code looks like this right now:

[WebMethod]
public string GenerateNumber()
{
    Random random = new Random();
    return random.Next(?);
}

**Update ended up doing like so,

[WebMethod]
public string GenerateNumber()
{
    Random random = new Random();
    string r = "";
    int i;
    for (i = 1; i < 11; i++)
    {
        r += random.Next(0, 9).ToString();
    }
    return r;
}

Solution 1

If you want ten digits but you allow beginning with a 0 then it sounds like you want to generate a string, not a long integer.

Generate a 10-character string in which each character is randomly selected from '0'..'9'.

Solution 2

Use this to create random digits with any specified length

public string RandomDigits(int length)
{
    var random = new Random();
    string s = string.Empty;
    for (int i = 0; i < length; i++)
        s = String.Concat(s, random.Next(10).ToString());
    return s;
}

Solution 3

try (though not absolutely exact)

Random R = new Random();

return ((long)R.Next (0, 100000 ) * (long)R.Next (0, 100000 )).ToString ().PadLeft (10, '0');

Solution 4

To get the any digit number without any loop, use Random.Next with the appropriate limits [100...00, 9999...99].

private static readonly Random _rdm = new Random();
private string PinGenerator(int digits)
{
   if (digits <= 1) return "";

   var _min = (int)Math.Pow(10, digits - 1);
   var _max = (int)Math.Pow(10, digits) - 1;
   return _rdm.Next(_min, _max).ToString();
}

This function calculated the lower and the upper bounds of the nth digits number.

To generate the 10 digit number use it like this:

PinGenerator(10)

Solution 5

private void button1_Click(object sender, EventArgs e)
{
   Random rand = new Random();
   long randnum2 = (long)(rand.NextDouble() * 9000000000) + 1000000000;
   MessageBox.Show(randnum2.ToString());
}

View more solutions

Comments

[Hriskesh Ashokan]

Did exactly this, my code looks like the updated block above.

[Caramiriel]

9999999999 overflows int.MaxValue, thus doesn't compile.

[Neil Masson]

How is this a random number?

[Danhol86]

Do not use this function if you intend on using it more than once. The random object should be declared outside the function scope as each time it will create a new instance of the Random object which can mean same number is generated. See stackoverflow.com/a/5264434/6099813

[EAmez]

Whenever you call this function, it will return a different value. That's almost like random value.This solution works for me: I only need to get different values each time I call it, no matter what the value is.

[Caboosetp]

@Danhol86 This does not have the same issue as the link you posted. What you posted specifies a seed in the constructor while this does not. If you do not specify a seed, a seed will be generated from the system clock which mostly guarantees different numbers. Still good to know about either way.

[Alparslan ŞEN]

I have tried 1 million times was successful(for lenght 15 digits)

[Wai Ha Lee]

This won't work for ten digits, as the range of values representable by int is ~±2*10^9 - so once min is 10^8 you'll overflow and get unexpected values for max.

[Captain Prinny]

What's the purpose of multiplying two numbers together instead of just doing a single multiplication?

[VSB]

It will not cover all 10 digit numbers. This method will not cover prime number in 10 digit number range.

[Lucas]

I'm not sure random has anything to do with range. You may be describing predictability rather than randomness?

[user1544428]

In certain circumstances, this code can produce duplicates. Do some research on it. I have had similar code that when used in a loop would work just fine, but move it to a faster computer and it return duplicates a few times in a row here or there. Quite annoying to track down. Also, a change in time or having multiple computers running the code. I'm just saying.