Avoiding implicit conversion in constructor. The 'explicit' keyword doesn't help here

Question

I am able to avoid the implicit conversion of a constructor using the explicit keyword. So now, conversions like A a1 = 10; can be avoided.

Answer 1

To avoid int->double conversions everywhere, not only in your case. With g++ you can use -Wconversion -Werror. Note that it'll be allowed in your particular case, because the compiler understands that 10.0 is literal, but it will fail compilation for:

class A
{
public:
    explicit A(int a)
    {
        num = a;
    }

    int num;
};

int main()
{
    double x = 10;
    A a1 = A(x);
    static_cast(a1);
    return 0;
}

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