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Random - Different Number that hasnt been drawn.

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Random - Different Number that hasnt been drawn.

May 19th, 2008

My appologies if this has been answered before but I couldnt find a specific answer/response.

Basically Im wondering how I would assure each random number is one that hasnt been produced already. In the program below Im trying to use the random number produced to act as a specific number of an array.

 Help with Code Tags 
 cpp Syntax (Toggle Plain Text) 
#include <iostream> 
#include <ctime>
#include <cstdlib>
 
using namespace std;
 
int main() 
{ 
int numb[4], n;
int numb2[4];
 
 
    srand((unsigned)time(0)); 
 
    int lowest=0, highest=3; 
    int range=(highest-lowest)+1; 
 
	numb2[0] = 10;
	numb2[1] = 11;
	numb2[2] = 12;
	numb2[3] = 13;
 
		for ( n=0 ; n<4 ; n++ )
		{
                numb[n] = lowest+int(range*rand()/(RAND_MAX + 1.0));
		cout << numb[n] << endl;
		cout << numb2[numb[n]] << endl;
		}
 
 
 
	system("pause");
}
#include <iostream> 
#include <ctime>
#include <cstdlib>

using namespace std;

int main() 
{ 
int numb[4], n;
int numb2[4];


    srand((unsigned)time(0)); 
  
    int lowest=0, highest=3; 
    int range=(highest-lowest)+1; 

	numb2[0] = 10;
	numb2[1] = 11;
	numb2[2] = 12;
	numb2[3] = 13;
   
		for ( n=0 ; n<4 ; n++ )
		{
                numb[n] = lowest+int(range*rand()/(RAND_MAX + 1.0));
		cout << numb[n] << endl;
		cout << numb2[numb[n]] << endl;
		}
		
	
	
	system("pause");
}

I tried a few if statements and a while loop to assure that if the number drawn is the same as one already drawn then re-do the random number but it wasnt happening.

Any ideas?

 Help with Code Tags 
 cpp Syntax (Toggle Plain Text) 
do 
{
  numb[2] = lowest+int(range*rand()/(RAND_MAX + 1.0));
}
while ((numb[2] == numb[1]) && (numb[2] == numb[3]) && (numb[2] == numb[0]));
do 
{
  numb[2] = lowest+int(range*rand()/(RAND_MAX + 1.0));
}
while ((numb[2] == numb[1]) && (numb[2] == numb[3]) && (numb[2] == numb[0]));

The reason I wish to know how to do this is because for a project I want to randomised the order of how certain strings are shown. I have already used a bubble sort but I was curious for this method.
Safe.

.........scaricamento.........

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Join Date: Aug 2005

Posts: 15,381

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Ancient Dragon Ancient Dragon is offline

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Re: Random - Different Number that hasnt been drawn.

May 19th, 2008

If you are wanting to contain an array of unique random numbers, then

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
for each element in the array
    generate a random number
    search the array to see if the number already exists
    if not, then add it to the array
    otherwise, if it was found then go back and generate another number
end of loop
for each element in the array
    generate a random number
    search the array to see if the number already exists
    if not, then add it to the array
    otherwise, if it was found then go back and generate another number
end of loop

// something like this

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 C++ Syntax (Toggle Plain Text) 
const int maxnums= 10;
int nums[maxnums] = {0};
int curnum = 0;
for(int i = 0; i < maxnums; ++i)
{
    bool found = false;
    do {
       int  x = rand();
       for(int j = 0; j < curnum && found == false; ++j)
       {
            if( nums[j] == x)
            {
                found = true;
            }
         }
        if(found == false)
       {
            nums[curnum++] = x;
       }
    } while(found == true);
}
const int maxnums= 10;
int nums[maxnums] = {0};
int curnum = 0;
for(int i = 0; i < maxnums; ++i)
{
    bool found = false;
    do {
       int  x = rand();
       for(int j = 0; j < curnum && found == false; ++j)
       {
            if( nums[j] == x)
            {
                found = true;
            }
         }
        if(found == false)
       {
            nums[curnum++] = x;
       }
    } while(found == true);
}

Last edited by Ancient Dragon; May 19th, 2008 at 12:45 pm.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Re: Random - Different Number that hasnt been drawn.

May 19th, 2008

Here is another way to do it

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <algorithm>
#include <ctime>
using namespace std;
 
int main()
{
 
    const int maxnum = 10;
    int nums[maxnum] = {0};
    srand((unsigned int)time(0));
    int curnum = 0;
    for(int i = 0; i < maxnum; ++i)
    {
        bool found = false;
        do
        {
            int x = rand() % 50;
            int* result = std::find(&nums[0], &nums[maxnum-1], x);
            if( *result < 0)
            {
                nums[curnum++] = x;
                found = true;
            }
        } while( found == false);
   }
    for(int i = 0; i < maxnum; ++i)
        cout << nums[i] << "\n";
 
}
#include <iostream>
#include <algorithm>
#include <ctime>
using namespace std;

int main()
{

    const int maxnum = 10;
    int nums[maxnum] = {0};
    srand((unsigned int)time(0));
    int curnum = 0;
    for(int i = 0; i < maxnum; ++i)
    {
        bool found = false;
        do
        {
            int x = rand() % 50;
            int* result = std::find(&nums[0], &nums[maxnum-1], x);
            if( *result < 0)
            {
                nums[curnum++] = x;
                found = true;
            }
        } while( found == false);
   }
    for(int i = 0; i < maxnum; ++i)
        cout << nums[i] << "\n";

}