Isbn Decoding Issue

int decode(FILE* fp, char* str, char* area, char* publisher, char* title){
    // determine area
    int area0;
    bool found = false;
    int digitsArea = 0;
    for (digitsArea = 1; digitsArea <= 5; digitsArea++) {
        // parse the first 'digits' chars in isbn into area0
        area0 = 0;
        for (int i = 0; i < digitsArea; ++i) {
            area0 = area0 * 10 + (str[i] - '0');
            cout << str[i] << endl; //debug output
        }
        if (registered(fp, area0)) {
            found = true;
            break;
        }
    }
    if (!found) {
        cout << "Area not found: " << area << endl;
        return false;
    }
    
    std::stringstream aout;
    aout << area0;
    aout >> area;

    // determine publisher
    int pub0, digitsPub = 0;
    for (digitsPub = digitsArea + 1; digitsPub <= 7; digitsPub++){
        //parse the second set of 'digits' chars in isbn into pub0
        pub0 = 0;
        for (int i = digitsArea; i < digitsPub; i++){
            pub0 = pub0 * 10 + (str[i] - '0');
            cout << str[i] << endl; //debug output
        }
        if (registered(fp, area0, pub0)){
            found = true;
            break;
        }
    }
    if (!found){
        cout << "Publisher not found: " << publisher << endl;
        return false;
    }
    
    std::stringstream pout;
    pout << pub0;
    pout >> publisher;

    // determine title
    int title0;
    for (int digitsTitle = digitsPub + 1; digitsTitle <= 10; digitsTitle++){
        //parse the third set of 'digits' chars in isbn into title0
        title0 = 0;
        for (int i = digitsPub; i < digitsPub; i++){
            title0 = title0 * 10 + (str[i] - '0');
            cout << str[i] << endl; //debug output
        }
    }
    
    std::stringstream tout;
    tout << title0;
    tout >> title;
    return true;
}

int registered(FILE* fp, int area, int publisher){
    seekStart(fp);
    ifstream in(fp);
    while (in) {
        int area0, minPublisher, maxPublisher;
        in >> area0 >> minPublisher >> maxPublisher;
        if (area0 == area) {
            if (minPublisher <= publisher && publisher <= maxPublisher) return true;
        }
    }
    return false;
}

int registered(FILE* fp, int area){
    seekStart(fp);
    ifstream in(fp);
    while (in) {
        int area0, minPublisher, maxPublisher;
        in >> area0 >> minPublisher >> maxPublisher;
        if (area0 == area) return true;
    }
    return false;
}