C# Join 2 Numbers (INT) into 1 longer INT

Question

It might be quite funny but I really didn't know how to search to find the answer for this one.

I always use something like this when I want to join strings "string = "something" + "somethingelse" "

but how to do it with INT? :)

Random r = new Random();
int lvfirst = r.Next(485924948);
int lvsecond = r.Next(39);
int lvdone = lvfirst + lvsecond;
Globals.GlobalInt = lvdone;

I tried doing one long int but it doesn't seem to work it says something about Long so if you can help me how to join this 2 random numbers into 1? I need 1 random number max "48592494839"

Thanks a lot!

Check this out: [random-number-in-long-range](http://stackoverflow.com/questions/6651554/random-number-in-long-range-is-this-the-way) — Zbigniew, Jul 07 '12 at 12:24
So what you really meant is "I need 1 random number max 48592494839", and the rest is just to ensure that you'll get bad answers? — harold, Jul 07 '12 at 12:31

Jon · Accepted Answer · 2012-07-07T12:31:31.313

2

There are two problems with this code:

"Sticking together" two outputs of Next will not give you a random value in the target range. Math does not work with strings.
Instead of returning a result it stores it in a global variable.

If you want a value in the range you specify, use

var result = (long) (r.NextDouble() * 48592494839);

This will still not work for any target range, but it will comfortably meet your specific requirements.

edited Jul 07 '12 at 12:31

answered Jul 07 '12 at 12:25

Jon

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`485,924,948` is smaller than Int32.MaxValue, which is `2,147,483,647`. – matthewr Jul 07 '12 at 12:32
@MatthewRz: I would have sworn I counted one digit more :) Thanks for the heads up, edited to correct. – Jon Jul 07 '12 at 12:33
I think this is perfect thank you for the code and for explaining I wasn't aware I had problem with the code =)! – MiLady Jul 07 '12 at 12:36
just another quick question now I have `var result = (long)(r.NextDouble() * 48592494839); Globals.GlobalLong = result;` if i like to add up or subtract this value how should I do it? `var addup = result + 25;` will be ok? – MiLady Jul 07 '12 at 12:47
1. this isn't a good way to get random numbers, what you'll get wont have any entropy. 2. concating two random numbers does produce one random number. – AK_ Jul 07 '12 at 12:49
@AK_: 1. Reference please? 2. It produces one *unpredictable* number, not one *random* number. If you concat two numbers randomly chosen from the range [1, 10] you will get an unknown result but it most certainly *will not* be a *random* number in the range [11, 1010]. You are clearly wrong here. – Jon Jul 07 '12 at 13:21
@Jon 1. for example, you will never get the number 16197498279, nor 9718498967, nor a lot of other results that should arise from numbers that double can't represent. 2. I was partially wrong here... if you take two numbers in [1,99] you will get a random number in the [11,9999] range... but it of course depends on the range... – AK_ Jul 07 '12 at 15:24
@AK_: First, that has nothing to do with entropy. Second, you are wrong because `double` [can represent any integer with magnitude <= 2^52](http://en.wikipedia.org/wiki/Double-precision_floating-point_format) which is a number much bigger than your examples. Third, it does not "depend on" anything. Math is math. – Jon Jul 07 '12 at 15:28
@Jon it cant represent any real number between 0 and 1 ... regarding the second point you should read my response again. – AK_ Jul 07 '12 at 15:36
@AK_: *Nothing* can represent **any** real in [0, 1] because there are infinite reals in that range. Do you have a point? – Jon Jul 07 '12 at 15:45

matthewr · Answer 2 · 2012-07-07T12:27:46.180

0

You could do something like this:

Random r = new Random();
int lvfirst = r.Next(485924948);
int lvsecond = r.Next(39);
long lvdone = Int64.Parse(lvfirst.ToString() + lvsecond.ToString());
Globals.GlobalInt = lvdone;

Basically we are converting all of the ints to a string which will append the second number to the end of the first number, then we convert it back to an int.

Hope this Helps!

edited Jul 07 '12 at 12:27

answered Jul 07 '12 at 12:22

matthewr

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Thank you for the help, it looks just like my type of coding =) and I like it! – MiLady Jul 07 '12 at 12:39

score 0 · Answer 3 · answered Jul 07 '12 at 12:24

Do you want to add or concatenate your ints ?

If you want to concatenate, you can try:

long lvdone = long.Parse(lvfirst.toString() + lvsecond);

If you want to add them and avoid overflows:

long lvdone = ((long) lvfist) + lvsecond

If you number must be arbitrarily long, try using Decimal instead of long

score -1 · Answer 4 · answered Jul 07 '12 at 12:45

Ignoring the random thing... this is the way to concat to numbers...

int a = 124;
int b = 101040507;

int digits = 32;
mask = 0x80000000;
while(a & mask == 0)
{
    digits--;
    mask= mask >> 1;
}


long result = b;
result = result << digits;
result = result | b;

C# Join 2 Numbers (INT) into 1 longer INT

4 Answers4