rand() function, to genetare a random number within the given set of numbers

Question

1.00/5 (2 votes)

See more:

hello,
i am a c++ beginner. i came across this question regarding rand function in c++. it wants us to program a code which generates a random number from a given set of numbers. i have herd about the rand() function but not about this feature regarding it!! i have already googled it!! but have not found a satisfying solution. please help me.

Posted 17-Aug-13 21:58pm

A.U.K

Add a Solution

3 solutions

Solution 2

I googled and this[^] was top of the list.

Posted 17-Aug-13 22:24pm

Richard MacCutchan

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2013-08-17T22:17:00

There are a couple of approaches you could use here:
The Brute-Force-And-Ignorance approach is to generate a random number using rand which is between the largest and smallest numbers in the valid set. If this number is in the set, use it. If it isn't, then generate another number and check again. This works, but...it's very slow, and may take an infinite time to generate a new number.

The best way to do it is to set up an array containing the set of valid numbers, and generate a number which is between zero and the number of items (minus one) using rand, and then use that number as an index to select a number from the array. This will take the same amount of time to select a number every time you try. And it can be extended to remove the number from the set so there are never duplicates, either - this is the way "intelligent" music players shuffle tracks for example, or the way to "shuffle" a pack of cards.

ridoy · Accepted Answer · 2013-08-17T22:38:00

Solution 3

I assume numbers is a set of given numbers.Then have a try with..

C++

int numbers[] = { 3, 13, 22, 57, 417 };
int length = sizeof(numbers) / sizeof(int);
int randomNumber = numbers[rand() % length];

Posted 17-Aug-13 22:38pm

ridoy

Comments

pasztorpisti 18-Aug-13 9:38am

+5, Although this is often not discrete uniform distribution that really doesn't matter in most cases.

ridoy 18-Aug-13 12:13pm

Thanks pasztorpisti,:).