Python-like string replace method for C++

preplace.cpp

#include <iostream>
#include <string>

int preplace(std::string& input, const std::string& a, const std::string& b){
    size_t index;
    int n = 0;
    while((index = input.find(a,0)) != std::string::npos){
        input.replace(index, a.size(), b);
        n++;
    }
    return n;
}

int main() {

    std::string myString = "How much wood would a woodchuck chuck if a woodchuck could chuck wood?";

    std::cout << myString << std::endl;

    preplace(myString, "wood", "rock");

    std::cout << myString << std::endl;

    return 0;
}