Conversion in Expressions

In an expression, C++ makes two kinds of automatic conversion. 1) Some type are automatically converted whenever they occur. 2) Some type are converted when they are combined with other types in an expression.
C++ converts bool, char, unsighed char, signed char and short to int. Because int type is generally chosen to be the computer’s most natural type. It can does calculations faster for that type. It’s called integer promotions.
unsigned short convert to int if short is shorter than int, if they have the same size. unsigned short convert to unsigned int. So no data loss in promoting.
short s1, s2, s //s1 and s2 convert to int first.
s = s1+s2; // then change int result back to short.
When an operation involves two types, the smaller is converted to the larger. Adding an int to a float, int is converted to float type. (You have to do it, because two types have the different inside representations)