Question

I’m trying to learn C from a Ruby/PHP/Java background, and I’ve found that you almost always explicitly cast things (at least in tutorials). Like, I always see things like

double x, y;
x = 1.0; 
/*...*/
y = x*5.0;

However, it seems that on my Mac’s version of GCC, automatic casting works.

Is leaving the .0 on things just a matter of style, or do some C compilers not autocast?

Answer 1

A constant has the type it is being assigned to:

int i = 1;
double x = 2; // 2.0

explicit cast:

i = (int)x;
x = (double)i;

implicit cast:

i = x;
x = i;

type promotion:

x = i / 2.0; // i is promoted to double before being multiplied
x = (double)i / 2.0; // so evaluates as this

vs

x = i / 2; // i is not promoted because 2 is an int
x = (double)( i / 2 ); // so evaluates as this