See this table on operator precedence to make things clearer. Simply put, a cast takes precedence over a division operation, so it would give the same output as
int s = ((double)t) / 2;
As knoight pointed out, this is not technically the same operation as it would be without the parentheses, since they have a priority as well. However, for the purposes of this example, it will offer the same result, and is for all intents and purposes equivalent.