int[] concat(int[] a, int[] b) {
    int la = length(a);
    int lb = length(b);
    int[] s = new int[la + lb];
    for(int i = 0; i < la; i++) {
        s[i] = a[i];
    }
    for(int i = 0; i < lb; i++) {
        s[i + la] = b[i];
    }
    return s;
}

int compare(int[] a, int[] b) {
    int l = length(a);
    if(l != length(b)) {   
        return false;
    }
    for(int i = 0; i < l; i++) {
        if(a[i] != b[i]) {
            return false;
        }
    }
    return true;
}

void toLower(int[] s) {
    int l = length(s);
    for(int i = 0; i < l; i++) {
        int c = s[i];
        if(c >= 'A' && c <= 'Z') {
            c = c - 'A' + 'a';
            s[i] = c;
        }
    }
}

void main() {
    int[] msg = "Hallo User: ";
    int[] name = "Kajetan";
    int[] together = concat(msg, name);
    int[] together2 = concat(together, name);
    test(together2);
    toLower(together);
    test(together);
    
    int[] a = name;
    test(a);
    test(a == name);
    
    int[] baum = "Kajetan";
    test(name == baum);
    test(compare(name, baum));
    test(compare(name, "Kajetan"));
    test(compare(name, "Kajetaa"));
}