Find subsequences of a string whose length is as large as 10,000

I have a string whose size can be as large as "10,000". I have to count those SUBSEQUENCES which are divisible by 9.

SUBSEQUENCE: A subsequence is an arrangement in which the order of characters of given string is maintained. For ex: if given string is 10292 then some of its subsequences are 1, 102, 10, 19, 12, 12(12 is twice as 2 comes twice), 129, 029, 09, 092, etc. Some numbers which are not subsequences of given string are: 201(2 and 0 can't come before 1), 921, 0291, etc.

I have tried to generate all subsequences(powerset) of given string using bit shifting and checking each string if it is divisible by 9. But this works fine as long as length of string is <=10. After that, I don't get proper subsequences(some subsequences are displayed negative numbers).

Below is my code:

    scanf("%s", &str); //input string 

    int n=strlen(str); //find length of string

    //loop to generate subsequences
    for(i=1;i<(1<<n);++i){

        string subseq;

        for(j=0;j<n;++j){

            if(i&(1<<j)){

                subseq+=str[j]; // generate subsequence
            }
        }

        //convert generated subseq to int; number is 'long' tpye
        number=atol(subseq.c_str());printf("%ld\n", number); 

        //ignore 0 and check if number divisible by 9
        if(number!=0&&number%9==0)count++;
    }

        printf("%ld\n", count);