Sorting class array in ascending order

Question

Quite new to programming and in need of some help, I'm looking to sort an class array in ascending order based on age, but I can only get the code to work in descending order. I may be overlooking something small since I've worked on this far too long so I'd appreciate any help!

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

class Person 
{
    public:
        string name;
        int age;
    
    
        Person(string name = "empty", int age = 0) 
        {
            setName(name);
            setAge(age);
        }
        void setName(string x) {
            name = x;
        }
        
        string getName() {
            return name;
        }
        void setAge(int y) {
            age = y;
        }
        int getAge() {
            return age;
        }
        void displayinfo()
        {
            cout << "Name: " << name; cout << " Age: " << age << endl;
        }
};
void swap(Person &p, Person &q)
{
 Person temp;
 temp.name = p.name;
 temp.age = p.age;
 p.name = q.name;
 p.age = q.age;
 q.name = temp.name;
 q.age = temp.age;
}

int main() 
{
    
    int userValue;
    Person po("Jessica", 24);
    Person po2("Robert", 49);
    Person po3("Maria", 47);
    Person po4("John", 19);
    Person family[4] = {po,po2,po3,po4}; 
    
    int sort(family[4].getAge()); 
    {
        for(int i = 0; i < 3; i++)
            if (family[i].getAge() < family[i+1].getAge()) 
            {
                swap(family[i], family[i+1]);
            }
        
    }
    for(int i = 0; i < 4; i++)
        family[i].displayinfo();

}

Answer 1

int sort(family[4].getAge()); is not a function declaration (and you can't implement a function inside of another function). It is actually a variable declaration. It is declaring a variable int sort that is initialized with the value from family[4].getAge() (which is undefined behavior since index 4 is out of bounds of your family[] array).

So, you are declaring an unused sort variable, and then you enter your for(int i = 0; i < 3; i++) loop, which DOES NOT perform a full sort of the array. For what you are attempting, use the standard std::sort() algorithm instead, eg:

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

class Person 
{
    public:
        string name;
        int age;
    
        Person(string name = "empty", int age = 0) 
        {
            setName(name);
            setAge(age);
        }

        void setName(string x) {
            name = x;
        }
        
        string getName() const {
            return name;
        }

        void setAge(int y) {
            age = y;
        }

        int getAge() const {
            return age;
        }

        void displayinfo() const
        {
            cout << "Name: " << name; cout << " Age: " << age << endl;
        }
};

int main() 
{
    Person po1("Jessica", 24);
    Person po2("Robert", 49);
    Person po3("Maria", 47);
    Person po4("John", 19);

    Person family[4] = {po1, po2, po3, po4};
    
    std::sort(family, family + 4,
        [](const Person &p1, const Person &p2) {
            return p1.getAge() < p2.getAge(); 
        }
    );

    for(int i = 0; i < 4; i++) {
        family[i].displayinfo();
    }

    return 0;
}

Live Demo

Note that your family[] array holds copies of the Person objects that you initialize it with. To avoid the overhead of those copies, you can sort pointers instead, eg:

int main() 
{
    Person po1("Jessica", 24);
    Person po2("Robert", 49);
    Person po3("Maria", 47);
    Person po4("John", 19);

    Person* family[4] = {&po1, &po2, &po3, &po4};
    
    std::sort(family, family + 4,
        [](const Person *p1, const Person *p2) {
            return p1->getAge() < p2->getAge(); 
        }
    );

    for(int i = 0; i < 4; i++) {
        family[i]->displayinfo();
    }

    return 0;
}

Live Demo

Or, you can get rid of the individual p0... objects altogether and initialize the array directly instead, eg:

int main() 
{
    Person family[4]{
        {"Jessica", 24},
        {"Robert", 49},
        {"Maria", 47},
        {"John", 19}
    };
    
    std::sort(family, family + 4,
        [](const Person &p1, const Person &p2) {
            return p1.getAge() < p2.getAge(); 
        }
    );

    for(int i = 0; i < 4; i++) {
        family[i].displayinfo();
    }

    return 0;
}

Live Demo