turing hep--- randomizing

[coolguy]

i want to make a program which shows # frm 0-9 in randomize order...it shuldn't duplicate any number.......need help

[Insectoid]

I believe this should have been posted in the 'help' section, but heck, I'll help anyway, I'm in a good mood.

To make a random number, us the Rand.Int command. This generates a number based on a complicated equation based on the current time (as a computer cannot produce anything with true randomness). The command is the following:

code:

variable := Rand.Int (smallestnumber, biggestnumber)

.

Now I'm going to assume you already know that, so I won't elaborate.

One way to do this is to create an extra variable as an array and set all of it to a number outside the scope of the random number (-1 or 10, in this case). Once you make a random number, add that into the array. Every time you create a new number, check through the array (in a for loop) for any occurence of that number. If that number has been used before, create a different number.

[coolguy]

var list : array 1 .. 10 of int
randomize
var random_number : int
for i : 1 .. 10
randint (random_number, 0, 9)

put random_number : 3 ..
end for



heres my code...wat do i change in this...

[Insectoid]

First, don't use randint, use Rand.Int. It's like the mature couson of randint. It's beneficial because it does not require a variable to work.

What you have so far is good. You just have to check to see if that nmber has been used before.

Use a for loop to initialize the array

code:

for x: 1..10      list (x) := -1 end for

Then, once you have created a random number, check if it's been used before.

code:

var numgood : boolean := true for x: 1..10      if random_number = list (x) then           numgood := false          end if end for

This is VERY inefficient and you'll only want to use it as a base from which to build.

[Saad]

Another way that is more simple, create an array of numbers from 1->10. Now in a loop, shuffle the numbers by swapping the numbers at 2 indexes. (Use Rand.Int to pick a random index for the two locations and swap them)

[riveryu]

@Saad

Do you mean using xor to switch the values? Can you give more of a hint?
like

Turing:

var a:int:=1 var b:int:=2 a:= a xor b b:= a xor b a:=a xor b put a put b

Can't Rand.Int repeat the same value when choosing 2 indexes, ex. you swap num(1) with (1) randomly.

[Tony]

well ideally the number stored in index 1 should have the same chance to appear in index 1 (so not be moved) as it has to appear in any other particular slot.

There are more efficient (and accurate) ways of generating random lists, then shuffling an array. Well, efficient in terms of CPU, it takes up twice as much memory. Though considering the size of the problem (10 elements? that's negligible)

[Rwed]

would you know how to randomize songs then?

[Tony]

You have a list of songs, and you randomly pick a position in that list.

[2goto1]

hit "shuffle" in your go-to media player and you're all set