DaniWeb Forum Index > Software Development > C++

C++ RSS

Duplication

Please support our C++ advertiser: Intel Parallel Studio Home

•

Join Date: Mar 2003

Posts: 1

Reputation: I0adidas0I is an unknown quantity at this point

Solved Threads: 0

I0adidas0I I0adidas0I is offline

Offline

Newbie Poster

Duplication

Mar 5th, 2003

OK I need some help... so far ive been able to get everything on my own but...im making a program that selects questions from an array numbered 1-40. i put in a random fuctions so the questions are chosen randomly. but i want to have it so that theres no duplication in the questions. like if the number is already chosen... skip and pick the next. any help would be much appreciated.

•

Join Date: Aug 2003

Posts: 37

Reputation: Xelfinn is an unknown quantity at this point

Solved Threads: 0

Xelfinn

Offline

Light Poster

Mar 6th, 2003

It seems easy enough to set up another array to store a reference of string pointers to the questions chosen. And each time a random question is selected search the other array for a matching pointer. Make sure you set each of the other array cells to NULL so you don't compare some unknown something.

Of course I don't know C++ but that's how I'd do it in C. I'd probably set the array only to 10 pointers and run it like a queue once it's filled up. A repeat after 10 questions wouldn't be bad.

•

Join Date: Feb 2002

Posts: 12,043

Reputation: cscgal is a glorious beacon of light

Solved Threads: 128

cscgal

Offline

The Queen of DaniWeb

Mar 6th, 2003

Here's an extremely simplistic/mediocre way of doing it in C++, based on Aelfinn's posted.

Lets say you have array of strings A[40] with 40 cells, that looks sorta like the following?

A[0] = Question 1?
A[1] = Question 2?
A[2] = Question 3?

and, well, you get the idea. Now, basically create a second array, int B[40]. Also create a variable int so_far which will be an accumulator each time a question is asked.

So, lets say a random number 5 is chosen. First, look up A[5] and ask the question. Then, set B[0] equal to 5, and increment so_far by 1. Now, lets say a random number 8 is chosen. Look up A[8], ask the question, and set B[1] equal to 8, and increment so_far by 2. Each time a question is asked, do a linear search on B[0] through B[so_far - 1] to see if any of the values match up to 8. Make sense?

Dani the Computer Science Gal

Follow my Twitter feed! twitter.com/DaniWeb
And if you're interested in Internet marketing there is twitter.com/DaniWebAds

•

Join Date: Feb 2003

Posts: 129

Reputation: Bob is an unknown quantity at this point

Solved Threads: 1

Bob

Offline

Team Member

Mar 7th, 2003

One easy way to achieve this would be as follows:

- Start with your array of 40 questions (strings).
- Initialise a counter to the number of strings (40)
- Select a random string in the range 1 to 40 (e.g. string 10)
- Swap the selected string (10) with the last unused string (40)
- Output string 40
- decrement the number of strings (to 39)

The string you used is now outside the range (as string 40)

- Select a random string in the range 1 to 39 (e.g. string 26)
- Swap the selected string (26) with the last unused string (39)
- Output string 39
- decrement the number of string to 38

The used strings are at positions 39 and 40, outside of the range

- repeat as required, handle the condition whereby zero strings are left

It sounds more complicated than it really is, here's a function that achieves it (using a vector of strings):

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
string getQuestion(vector<string>& v, int& numberOfStrings)
{
    // handle errors
    if(numberOfStrings <= 0) return "error";
    if(numberOfStrings > v.size()) return "error";
 
    // select a random number in the range 0 - numberOfStrings-1
    int next = rand() % numberOfStrings;
 
    // decrement the number of strings
    numberOfStrings--;
 
    // swap it with the last unused string
    swap(v[next], v[numberOfStrings]);
 
    // retrieve the string
    return v[numberOfStrings];
}
string getQuestion(vector<string>& v, int& numberOfStrings)
{
    // handle errors
    if(numberOfStrings <= 0) return "error";
    if(numberOfStrings > v.size()) return "error";

    // select a random number in the range 0 - numberOfStrings-1
    int next = rand() % numberOfStrings;

    // decrement the number of strings
    numberOfStrings--;
    
    // swap it with the last unused string
    swap(v[next], v[numberOfStrings]);
    
    // retrieve the string
    return v[numberOfStrings];
}

You populate your vector with strings, then set an integer variable equal to the number of strings, and off you go - make calls to the getQuestion() function.

Here's a demo program:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
#include <algorithm>
 
using namespace std;
 
string getQuestion(vector<string>& v, int& numberOfStrings)
{
    if(numberOfStrings <= 0) return "Error";
    if(numberOfStrings > v.size()) return "Error";
 
    int next = rand() % numberOfStrings;
    numberOfStrings--;
    swap(v[next], v[numberOfStrings]);
    return v[numberOfStrings];
}
 
int main()
{
    vector<string> q;
 
    q.push_back("One");
    q.push_back("Two");
    q.push_back("Three");
    q.push_back("Four");
    q.push_back("Five");
    q.push_back("Six");
    q.push_back("Seven");
    q.push_back("Eight");
    q.push_back("Nine");
    q.push_back("Ten");
 
    int num=q.size();
 
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
}
#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
#include <algorithm>

using namespace std;

string getQuestion(vector<string>& v, int& numberOfStrings)
{
    if(numberOfStrings <= 0) return "Error";
    if(numberOfStrings > v.size()) return "Error";

    int next = rand() % numberOfStrings;
    numberOfStrings--;
    swap(v[next], v[numberOfStrings]);
    return v[numberOfStrings];
}

int main()
{
    vector<string> q;

    q.push_back("One");
    q.push_back("Two");
    q.push_back("Three");
    q.push_back("Four");
    q.push_back("Five");
    q.push_back("Six");
    q.push_back("Seven");
    q.push_back("Eight");
    q.push_back("Nine");
    q.push_back("Ten");
    
    int num=q.size();
    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
    cout << getQuestion(q,num) << endl;    
}

•

Join Date: Aug 2003

Posts: 37

Reputation: Xelfinn is an unknown quantity at this point

Solved Threads: 0

Xelfinn

Offline

Light Poster

Mar 7th, 2003

I like that...much faster than my idea and with no guaranteed work to prove the string hasn't been used.

•

Join Date: Feb 2003

Posts: 129

Reputation: Bob is an unknown quantity at this point

Solved Threads: 1

Bob

Offline

Team Member

Mar 8th, 2003

Note that you'd want to add a call to srand() at the start of main() in your program. It suited me not to do this during testing so that it always used the same sequence.