How to avoid repetition of random numbers in C++?

Question

Example
This code:
srand(time(0));
for(int x=0;x<5;x++)
{
int r=rand()%5;
cout<<r<<" ";
}

Output
0 3 2 3 1

But i want to avoid the repetition and i want the output to be :
4 2 3 1 0

Any idea ?

Answer 1

I think what you should be asking is, "How do I shuffle the list {0,1,2,3,4}". This is not so much about generating random numbers, you are actually trying to find a so-called "permutation of a list"!

And, C++ can do it for you:

#include <iostream>
#include <algorithm>
#include <iterator>

int main () {

using namespace std;

int v[] = {0,1,2,3,4};
random_shuffle(begin(v), end(v));

for(int i : v)
cout << i << endl;

}

If you want to "do it yourself", you can google the Fisher-Yates algorithm to shuffle a list. It's really simple actually!

I see what you were going for in your code and it almost works. One problem is that your for loop probably needs to run a lot more often than 5 times though (it's random how often).

Answer 2

Keep track of already used numbers by using Array and check Everytime if new generated number is in array or not

Answer 3

I tied but doesn't work

Answer 4

Show me your try, then I can figure out what is problem 😉

Answer 5

int a[]={1,2,3,4,5};
srand(time(0));
for(int x=0;x<5;x++)
{
int c=rand()%5;
int b=rand()%5;
if(c==b)
{}
else{cout<<a[c];}
}

Answer 6

Woah thank you so much man 👍👍👍👍👍👍