Unıque Random Number Check form Array c++

#include <iostream>
#include<ctime>
#include<cstdlib>
#include<string>
#include<cmath>

using namespace std;

int main()
{
    bool cont=false;
    string str;
    int num,num2;
    cin >> str >> num;
    int arr[10];

    int a = pow(10,num);
    int b=  pow(10,(num-1));
srand(static_cast<int>(time(NULL)));

    do{


    num2=rand()%(a-b)+b;
    int r;
    int i=0;
    int cpy=num2;

while(cpy!=0){

        r=cpy%10;
        arr[i]=r;
        i++;
        cpy=cpy/10;


    }

     for (int m=0; m<num; m++)
    {

        for (int j=0; j<m; j++){
                if(m != j){
               if (arr[m] == arr[j]){

                           break;



                        }
                        else{
                            cont=true;

                        }

                }



           }


    }
    cout<<num2<<endl;
    }while(!cont);

    return 0;
}

I want to take a number from the user and produce such a random number.

For example, if the user entered 8, an 8-digit random number.This number must be unique, so each number must be different from each other,for example:

user enter 5

random number=11225(invalid so take new number)

random number =12345(valid so output)

To do this, I divided the number into its digits and threw it into the array and checked whether it was unique, but I get an error.How can I solve the problem?