Why the following programs will cause error? #include <iostream> #include <string> using namespace std;class Box { int capacity; public: Box(int cap){ capacity = cap; } friend void show(); }; void Box::show() { Box b(10); cout<<"Value of capacity is: "<<b.capacity<<endl; } int main(){ show(); return 0; }

The program will cause an error because the `show()` function is defined outside of the `Box` class but is not declared as a friend function inside the class. To fix it, you can add a friend declaration inside the class like this:

class Box {
    int capacity;
public:
    Box(int cap){ capacity = cap; }
    friend void show();
};

void show() {
    Box b(10);
    cout<<"Value of capacity is: "<<b.capacity<<endl;
}

int main(){
    show();
    return 0;
}

Alternatively, you can define the `show()` function inside the `Box` class like this:

class Box {
    int capacity;
public:
    Box(int cap){ capacity = cap; }
    void show() {
        cout<<"Value of capacity is: "<<capacity<<endl;
    }
};

int main(){
    Box b(10);
    b.show();
    return 0;
}