Why is the sum of an int and a float an int?

Question

Consider the following code:

float d  = 3.14f;
int   i  = 1;
auto sum = d + i;

According to cppreference.com, i should be converte

Answer 1

It's rather simple really.

In old versions of C (before C99), you could write something like

auto n = 3;

and n would be an int type with the value 3. You could also write

auto n = 3.14f;

and n would still be an int type, with a value 3.

This was called implicit int and K & R made it quite famous.

So can you see that

auto sum = d + i;

merely assigns the float type d + i to sum which is an implicit int.

Hence the answer 4.

In newer versions of C (C99 onwards), implicit int was dropped.