something wrong with the output

[Ahmed Sayed]

I'm solving a problem that make me generate a password depends on some rules,

1-the length of the password must be equal to n,
2-the password should consist only of lowercase Latin letters,
3-the number of distinct symbols in the password must be equal to k,
4-any two consecutive symbols in the password must be distinct.

and i wrote the algorithm, but when i put the input (n=5,k=2)
the output must be "ababa" but i get "abab" and the last character is strange

#include <iostream>
#include <string>
#include <cstring>

using namespace std;
int main()
{
    char arr[26]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
    char allow[26];
    int n,k,m=0;
    string pass="";
    cin >> n >> k;

    for (int i=0;i<k;i++){
        pass+=arr[j];
        allow[i]=arr[j++];

    }
    for (int i=0;i<n-k;i++){

        if (m==strlen(allow)){
            m=0;
        }
        else{
            pass+=allow[m++];
        }
    }
    cout << pass ;

    return 0;
}

[lastchance]

Declare and initialise j.

strlen(allow) can be replaced by k.

Remove lines 24 and 26.

[Ahmed Sayed]

Thanks man,it worked
but can you tell me why strlen() function didn't work !

[lastchance]

strlen() relies on the string being null-terminated and you don't explicitly do that. I suspect it comes down to undefined behaviour, as the characters in allow[] aren't set on declaration in line 9. It is just plausible that they might initially be \0, in which case your code might fortuitously run, but don't rely on it.