c# - System.Convert.ToInt vs (int)

Question

I noticed in another post, someone had done something like:

double d = 3.1415;
int i = Convert.ToInt32(Math.Floor(d));

Why did they use the convert function, rather than:

double d = 3.1415;
int i = (int)d;

which has an implicit floor and convert.

Also, more concerning, I noticed in some production code I was reading:

double d = 3.1415;
float f = Convert.ToSingle(d);

Is that the same as:

float f = (float)d;

Are all those otherwise implicit conversions just in the Convert class for completeness, or do they serve a purpose? I can understand a need for .ToString(), but not the rest.

Answer 1

Casting to int is implicit truncation, not implicit flooring:

double d = -3.14;
int i = (int)d;
// i == -3

I choose Math.Floor or Math.Round to make my intentions more explicit.