copy constructor does initialize primitive data types

#include <iostream>

using namespace std;

class Foo
{
public:
        int a;
};
int main()
{
        Foo f;
        Foo f1(f);
        cout<<f.a;
        return 0;
}

Here f.a prints garbage value but when we add f1.a then both f.a and f1.a is initialized with 0.

#include <iostream>

using namespace std;

class Foo
{
public:
        int a;
};
int main()
{
        Foo f;
        Foo f1(f);
        cout<<f.a<<f.b;
        return 0;
}

Please help me to understand what is the reason behind this.