Random oddity
Recently I wrote a program to reshuffle data in a csv file. And I ran into a problem with Random in C#.
Let’s look at the following program. One would think that it should print 5 integers, randomly picked between 0 and 8. But no, in almost all cases, the program prints the same integer 5 times.
using System;
class Scaffolding
{
static void Main(string[] args)
{
for (int i = 0; i < = 5; ++i)
{
Random randomNumber = new Random();
Console.WriteLine(randomNumber.Next(9));
}
}
}
It turns out the correct way, and more efficient way according to documentation, is to instantiate one static Random class to generate many random numbers over time, instead of repeatedly creating a new Random to generate one random number, like so:
using System;
class Scaffolding
{
static Random randomNumber = new Random();
static void Main(string[] args)
{
for (int i = 0; i <= 5; ++i)
{
Console.WriteLine(randomNumber.Next(9));
}
}
}
MSDN documentation is here.