C++ Person Class - Unable to Output Values & Modify Element

Question

I am attempting to create a Person class that has values: string name, int age, int height, int weight. I am supposed to instantiate a Person object, give it values, and output those values. Also, I am supposed to have a ModifyPerson function that accepts a Person object as argument, and change the name member variable and output it. Any help would be greatly appreciated.

EDIT: Only issue I currently have with code is properly outputting the member values of person1

EDIT2: Fixed! Thank you Zebrafish

    #include <iostream>
    #include <string>
    using namespace std;

    class Person 
    {
        string name;
        int age, height, weight;
    public:
        void set_values(string, int, int, int);
        string ModifyPerson();
        void coutDetails() const;
    }person1;

    void Person::set_values(string a, int b, int c, int d) 
    {
        name = "Rob";
        age = 19;
        height = 71;
        weight = 180;
    }

    string Person::ModifyPerson()
    {
        string name = "Robert";
        return name;
    }

    void Person::coutDetails() const
    {
        cout << "\nName: " << name << "\nAge: " << age << "\nHeight: " <<         
        height << "\nWeight: " << weight;
    }

    std::ostream& operator<<(const std::ostream&, const Person& person1)
    {
        person1.coutDetails();
        return std::cout;
    }

    int main()
    {
        Person person1;
        person1.set_values("Rob", 19, 71, 180);
        cout << person1 << endl;
        cout << person1.ModifyPerson() << endl;
        return 0;
    }

Answer 1

The reason this line fails:

cout << person1 << endl;

Is told by the error message:

'<<': no operator found which takes a right-hand operand of type 'Person' (or there is no acceptable conversion)

std::cout, which is an std::ostream object doesn't have an operator << taking a Person object, unless you specifically create one.

The second cout line:

cout << person1.ModifyPerson() << endl;

Fails for a different reason. You definitely have the method ModifyPerson() in your class Person, but there's two problems with it:

1) The return types are different

2) You have defined ModifyPerson() as a global function, not a member class method.

So you need to make sure the return types are the same, and when you define the ModifyPerson() method you should place name of the class before hand, like this:

string Person::ModifyPerson(){}

I have a feeling you already knew this because you prefaced the method set_values with Person::

The code should look something like this:

#include <iostream>
#include <string>
using namespace std;

class Person
{
    string name;
    int age, height, weight;

public:
    void set_values(string, int, int, int);
    string ModifyPerson();
}person1;

void Person::set_values(string a, int b, int c, int d)
{
    name = "Rob";
    age = 19;
    height = 71;
    weight = 180;
}

string Person::ModifyPerson()
{
    string name = "Robert";
    return name;
}

int main()
{
    Person person1;
    person1.set_values("Rob", 19, 71, 180);
    //cout << person1 << endl;
    cout << person1.ModifyPerson() << endl;
    return 0;
}

Also if you want to be able to write cout << person1 you will need write a global function that takes an std::ostream as the first argument, like:

std::ostream& operator<<(const std::ostream&, const Person& person)
{
    person.coutDetails();
    return std::cout;
}

The coutDetails() method of the Person can look like this:

void Person::coutDetails() const
{
    cout << "\nName: " << name << "\nAge: " << age << "\nHeight:" <<
        height << "\nWeight: " << weight;
}

Edit: I noticed you changed your ModifyPerson function since I wrote this answer. That part of it only applies to your original post.