How can i write this code in C++ in an easy way ???the formate is like the dark picture

#include #include using namespace std; string function (string str); int main() { return 0; string function(string str) { Problem 8: (5 pts): write a function that takes as an input parameter an integer (a large one!) The function should add the digits in the number together and return that integer. Input: 3248->17 Input: 823->13 Input: 1240293->21