Chapter 2 Page 43

saadis01 · May 17th, 2014, 05:59 PM

Why is the outer loop used here? The following code is generating 6 random numbers 49 times, yet at the end only 6 numbers are written out.

Code:

// pick 6 random numbers
for (int limit = 0; limit < 49; limit++)
{
for (int select = 0; select < 6; select++)
{
picked[select] = range[rnd.Next(49)];
}

}
Console.WriteLine("Your lotto numbers are:");
for (int j = 0; j < 6; j++)
{
Console.Write(" " + picked[j] + " ");
}

Rod Stephens · May 17th, 2014, 08:07 PM

I didn't write that chapter, so I can't be absolutely sure. But the text says the example demonstrates nested loops. You're right, however, that the outer loop doesn't really do anything so it's sort of a trivial example. (One might think picking the numbers 49 times would make it "more random," but it really doesn't.)

Here's a slightly more interesting example. It picks 10 sets of 6 numbers, assuming you're going to buy 10 lotto tickets.

Code:

// Make 10 picks.
for (int pick = 0; pick < 10; pick++)
{
    Console.WriteLine("Pick " + pick + ": ");
    for (int select = 0; select < 6; select++)
    {
        Console.Write(rnd.Next(49) + " ");
    }
    Console.WriteLine();
}

Even this one doesn't guarantee that the picks don't duplicate each other. For example, one set of six numbers might include the same number twice.

Still, it's good enough to demonstrate nested loops. (If you want to know how to avoid that, reply and I'll show you.

)

Rod Stephens · May 18th, 2014, 11:32 AM

Okay, I got interested in this and wrote up this solution. (Note the use of LINQ's Enumerable.Range method to generate the initial values 1 to 49.)

Code:

// Initialize the array of values between 1 and 49.
int[] values = Enumerable.Range(1, 49).ToArray();

// Make a random number generator.
Random rnd = new Random();

// Make 10 picks.
for (int pick = 0; pick < 10; pick++)
{
    // Randomize the first 6 values.
    for (int i = 0; i < 6; i++)
    {
        // Pick a value between position i and the last position.
        int j = rnd.Next(i, 48);

        // Swap the values in positions i and j.
        int temp = values[i];
        values[i] = values[j];
        values[j] = temp;
    }

    // Display the results.
    Console.Write("Pick " + pick + ": ");
    for (int i = 0; i < 6; i++)
    {
        Console.Write(values[i] + " ");
    }
    Console.WriteLine();
}

This is a lot more work than the simple nested loops that the chapter wanted to demonstrate, but I think it's interesting.

saadis01 · May 18th, 2014, 01:56 PM

I guess that's what was missing, if you are generating all those number, might as well print them out :)