Ivor Horton's Beginning Visual C++ 2012

TYPE CONVERSION AND CASTING

Calculations in C++ can be carried out only between values of the same type. When you write an expression involving variables or constants of different types, for each operation to be performed, the compiler has to arrange to convert the type of one of the operands to match that of the other. This process is called implicit type conversion. For example, if you want to add a double value to a value of an integer type, the integer value is first converted to double, after which the addition is carried out. Of course, the variable that contains the value to be converted is, itself, not changed. The compiler will store the converted value in a temporary memory location, which will be discarded when the calculation is finished.

There are rules that govern the selection of the operand to be converted in any operation. Any expression to be calculated breaks down into a series of operations between two operands. For example, the expression 2*3-4+5 amounts to the series 2*3 resulting in 6, 6-4 resulting in 2, and finally 2+5 resulting in 7. Thus, the rules for converting the type of operands where necessary need to be defined only in terms of decisions about pairs of operands. So, for any pair of operands of different types, the compiler decides which operand to convert to the other considering types to be in the following rank from high to low:

1. long double	2. double	3. float
4. unsigned long long	5. long long
6. unsigned long	7. long
8. unsigned ...