Function Overloading - Amiguity

[Cheddar99]

I know this will be simple for someone, but I would appreciate some insights as I don't quite understand what's going on.

I'm just playing with some code I created, and added two functions, per the code below. But, despite explicitly expressing each value in the function calls with L (long) and F (float) the compiler vomits it back up, telling me "...call of overloaded 'calc(long double)' is ambiguous".

#include <iostream>
using namespace std;
    
int calc(long x) {
return x * 2;
}

int calc(float y) {
return y * 2;
}

int main() {
cout << calc(100.0L) << calc(1.5F) << endl;
return 0;
}

In function 'int main()':
13:20: error: call of overloaded 'calc(long double)' is ambiguous
13:20: note: candidates are:
4:5: note: int calc(long int)
8:5: note: int calc(float)

Could somebody explain exactly why it doesn't work as I'm thinking it should do? Much appreciated! Thanks.

[mbozzi]

The literal 100.0 has type double.
If you add the "L" suffix to a double literal, you get a long double literal.

The error occurs because the compiler cannot decide whether to squeeze a long double into a float, or squeeze long double into a long. Either conversion throws away information, because there are values of long double that cannot be represented by float or long int. Such conversions are called narrowing conversions.

If you want a variable with type long, say 100l instead of 100.0l.

At some point, read
https://en.cppreference.com/w/cpp/language/integer_literal
and
https://en.cppreference.com/w/cpp/language/floating_literal
Every C++ programmer should know how to read and write numbers. (There are quite a few formats.)

[Cheddar99]

Thanks for the explanation @mbozzi. I'll read the info' at the links.