Exception Handling - General Questions

Why should exceptions usually be caught by const reference?

What will be the output of the program?

#include <iostream>
using namespace std;
#include <stdexcept>
int main() {
    try {
        throw out_of_range("bad index");
    } catch (const exception &e) {
        cout << e.what() << endl;
    }
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;
void f() { throw 5; }
void g() { f(); cout << "g"; }
int main() {
    try { g(); } catch (int v) { cout << v; }
    cout << endl;
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;

int main() {
    try {
        throw 42;
    } catch (int e) {
        cout << "int " << e << endl;
    } catch (...) {
        cout << "other" << endl;
    }
    return 0;
}

What does noexcept on a function indicate?