What will be printed out as a result of the follow

What will be printed out as a result of the following code execution?

#include <iostream>
class A {
public:
    explicit A(int _k = 10) {k = _k;}
    int k;
};
 
int main() {
    A a = int(100);
    std::cout << a.k;  
}

100
10
Compilation error will occur
Runtime error will occur

Explanation

Compilation error will occur because of the following. Since default constructor is declared with an explicit modifier, it will not serve as a type conversion constructor.