convert double to int

if you use cast, that is, (int)SomeDouble you will truncate the fractional part. That is, if SomeDouble were 4.9999 the result would be 4, not 5. Converting to int doesn't round the number. If you want rounding use Math.Round

The best way is to simply use Convert.ToInt32. It is fast and also rounds correctly.

Why make it more complicated?

Yeah, why not?

double someDouble = 12323.2;
int someInt = (int)someDouble;

Using the Convert class works well too.

int someOtherInt = Convert.ToInt32(someDouble);

You can use a cast if you want the default truncate-towards-zero behaviour. Alternatively, you might want to use Math.Ceiling, Math.Round, Math.Floor etc - although you'll still need a cast afterwards.

Don't forget that the range of int is much smaller than the range of double. A cast from double to int won't throw an exception if the value is outside the range of int in an unchecked context, whereas a call to Convert.ToInt32(double) will. The result of the cast (in an unchecked context) is explicitly undefined if the value is outside the range.