Multiple inheritance basic program C++

Multiple inheritance basic program in C++

#include <iostream>
using std::cout;

class b1{
int x;
public:
b1(int = 0);
int get();
};
b1::b1(int u){
x = u;
cout << "B1 constructor\n";
}
int b1::get(){
return x;
}

class b2{
int x;
public:
b2(int = 0);
int get();
};
b2::b2(int u){
x = u;
cout << "B2 constructor\n";
}
int b2::get(){
return x;
}

class a: public b1, public b2{
int x;
public:
a(int u = 0);
};
a::a(u){
x = u;
cout << "A constructor\n";
}

int main(){
a o;
reuturn 0;
}