random

[raphaelf]

Hello everybody,

I have some numbers, for example 16, 20, 23, 40, 43

I need to generate a random number of only this numbers i have.

How could i make this on QT or C++ ??

Can somebody help me?


For the moment i have this:

int max;
	QSqlQuery count("select count(words_id) from words_tbl");
	while(count.next())
	{
		max = count.value(0).toInt();
	}
 
	//random
	int a = (1 + ( rand() % ( max - 1 + 1 ) )); 
	QString b = QString::number(a);

int max;
	QSqlQuery count("select count(words_id) from words_tbl");
	while(count.next())
	{
		max = count.value(0).toInt();
	}
	
	//random
	int a = (1 + ( rand() % ( max - 1 + 1 ) )); 
	QString b = QString::number(a);

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[wysota]

This is smart enough

int fnc(){
  static int nmbrs[] = {16, 20, 23, 40, 43};
  int r = rand() % 5; // use something smarter than modulo here
  return nmbrs[r];
}

int fnc(){
  static int nmbrs[] = {16, 20, 23, 40, 43};
  int r = rand() % 5; // use something smarter than modulo here
  return nmbrs[r];
}

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[raphaelf]

uau
Thank you very much, you can think digital very well

[raphaelf]

Hi everybody,

With following sql statement i am able to rand a id from my database..
Its works, but the number 1 come every 3. time i run it

Have somebody a idea how to solve this by this sql statement?
If it possible i would like to rand a id with sql..

QString random;
	QSqlQuery count("SELECT words_id FROM words_tbl WHERE rowid>=random() % (SELECT max(words_id)+1 FROM words_tbl) LIMIT 1;");
 
	while(count.next())
	{
		random = count.value(0).toString();
	}

QString random;
	QSqlQuery count("SELECT words_id FROM words_tbl WHERE rowid>=random() % (SELECT max(words_id)+1 FROM words_tbl) LIMIT 1;");
	
	while(count.next())
	{
		random = count.value(0).toString();
	}

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[wysota]

Do you initialise the random number generator for your sql server with a pseudorandom seed? Moreover, as I said, modulo is not the best operator here... How many rows to you have in that table?

http://www.desilva.biz/mysql/random.html
http://forums.devarticles.com/mysql-...l-rows-16.html
http://www.tech-recipes.com/postgres...l_tips470.html
http://www.powerpostgresql.com/Random_Aggregate

[raphaelf]

Hi wysota,
I have on my sqlite database at the moment 250 rows, but the database will grow slowly..

My sended script works good, but just the number 1 repeat a lot..
The best solution for me would be that random numbers never repeats..

Have you a idea how to rand a number, and until my app is runing is not possible to rand a same number?

Thanks

[wysota]

I have on my sqlite database at the moment 250 rows, but the database will grow slowly..

My sended script works good, but just the number 1 repeat a lot..
The best solution for me would be that random numbers never repeats..

What if you run the lottery 251 times?

Have you a idea how to rand a number, and until my app is runing is not possible to rand a same number?

You can create a table with numbers 1-250 sequenced randomly and then when you want a random number, take a random row, remove it from the table and return the result. But again, what will happen if you want to have 251 random numbers?

[raphaelf]

Hi wysota its a great idea..

If i would run 251 i will get 0 probally?

[wysota]

If i would run 251 i will get 0 probally?

You won't get anything.

[raphaelf]

Hi Wysota, thats ok for my app..

Thank you, i will try it