# Qbasic: Generating 20 unique random numbers between 1 and 80 inclusive

Hi,
Im developing a small program using QBASIC.

How can I generate 20 unique random numbers between 1 and 80 inclusive. The numbers must be unique which means if the number 5 is picked it must be unable to come out again. (eg: like lotto or bingo)

Can anyone help me?

Regards
Mitch
LVL 2
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Commented:
have an array indexed 1 to 80.

generate random number between 1 to 20 (you can mod for limiting) , say N, check Array[N] is zero, if so change into 1 and increase a count, if not so, generate another random number and follow same above process.

do the same process till you reach 20 in count.
Commented:
Also use randomize to seed the random number generator before you start.

The random number routine is called rnd.
Commented:
High School Computer Science, Computer Applications, and Mathematics TeachersCommented:
I still have QB4.5 on my puter here...though I literally can't remember the last time I opened it!  =)

Here is a tested QB4.5 example of ozo's algorithm above...

It's messy...because I couldn't remember how to properly return an Array from a Function in QB4.5.
(this code would actually work in VB6 with one tiny change: "Print" becomes "Debug.Print")
``````RANDOMIZE TIMER

DIM i AS INTEGER
DIM count AS INTEGER
DIM index AS INTEGER
DIM tmp AS INTEGER

DIM min AS INTEGER
DIM max AS INTEGER
DIM numToSelect AS INTEGER

min = 1
max = 80
numToSelect = 20

' Populate numbers Array
count = max - min + 1
REDIM numbers(1 TO count) AS INTEGER
FOR i = 1 TO count
numbers(i) = min + (i - 1)
NEXT

' Shuffle the numbers Array
FOR i = 1 TO count
index = INT(RND * count) + 1
tmp = numbers(i)
numbers(i) = numbers(index)
numbers(index) = tmp
NEXT i

' Populate the Selections Array
REDIM Selections(1 TO numToSelect) AS INTEGER
FOR i = 1 TO numToSelect
Selections(i) = numbers(i)
NEXT

' Display the selections
FOR i = LBOUND(Selections) TO UBOUND(Selections)
PRINT i, Selections(i)
NEXT i
``````

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Commented:
> generate 20 unique random numbers between 1 and 80

a) Take an array from 1-80 and initialize to zero or false.
Pull a random number and flag its position in the array as found (set to a one or to true) - only if it was not set, otherwise you cannot count it as a successful toss.
- this metod wil run for 20 random tosses plus additional tosses for each one that duplicates another

b) Take an array from 1-80 and initialize from one to eighty in sequence
Toss a random from 1-80
From the position of the toss read the value of the element of array for the result
swap into that position of the array the value of the 80th item
For the next roll of random, only toss for value between 1-79
- this method always uses exactly 20 random numbers

Commented:

- Create an array A of integer with 80 elements

- populate it with numbers between 1 and 80

- for n times (with n great at your pleasure, i.e 200)
generate two random numbers (i,j) between 1 and 80
if (i<>j) swap position i and j of A

- take the first 20 numbers of the array

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