Question

I have in C++ an array of 100 elements, so v[1], … ,v[100] contains numbers. How can i display, 25 random numbers from this array? So i wanna select 25 random positions from this array and display the values.. How can i do this in C++?

Thanks!

    #include <cstdlib>
#include <iostream>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <vector>

using namespace std;
int aleator(int n) 
{
    return (rand()%n)+1;
}
int main() 
{
    int r;
    int indexes[100]={0};
  //  const int size=100;
    //int a[size];
    std::vector<int>v;
    srand(time(0)); 
    for (int i=0;i<25;i++) 
    {
     int index = aleator(100);
     if (indexes[index] != 0)      
    {
        // try again
         i--;
         continue;
     }
    indexes[index] = 1;
    cout << v[index] ;
    } 
    cout<<" "<<endl;
    system("pause");
    return 0;
}

The idea is that i have this code, and i generate 100 random numbers. What i want is an array with random 25 elements from those 100 generated.. But i don’t know how to do that

Regards

Answer 1

I modified the version of Mehdi a little in order to make it choose differnet indexes
NOTE: This makes the algorithm not deterministic – it relies on the RNG.

int indexes[100]={0};

srand ( time (0) );

for (int i=0;i<25;i++)
{
     int index = rand() % 100;
     if (indexes[index] != 0)
     {
         // try again
         i--;
         continue;
     }
     indexes[index] = 1;
     cout << v[index] ; cout << endl;
}