c++: Write a recursive function to_number that forms the integer sum of all digit characters in a string. For example, the result of to_number("3ac4") would be 7.Hint: If next is a digit character ('0' through '9'), function is_digit(next) in header will return true. What I have does not work. Is there a way to fix it?

#include #include #include

using namespace std;

int to_number (string s) { //int isdigit();

if (s == " " || s.length() == 0) { return 0; } char next = s.string::at(0); if (std::isdigit(next) == true) { return isdigit(next) + to_number(s.string::substr(1)); } else { return to_number(s.string::substr(1)); } }

int main() { string s; cout << "Enter string. "; cin >> s; cout << to_number << endl; system("pause"); }