c++ string to double

To convert a C++ string to a double, you can use the `std::stod` function from the `<string>` header. Here's an example:

#include <iostream>
#include <string>

int main() {
    std::string str = "3.14";
    double num = std::stod(str);
    std::cout << "Converted double value: " << num << std::endl;
    return 0;
}

In this example, the `std::stod` function is used to convert the string `"3.14"` to a double value. The resulting value is stored in the variable `num` and then printed using `std::cout`.