HP C A.06.05 Reference Manual

Chapter 4 75
4 Type Conversions
The use of different types of data within C programs creates a need for data type conversions.
For example, some circumstances that may require a type conversion are when a program
assigns one variable to another, when it passes arguments to functions, or when it tries to
evaluate an expression containing operands of different types. C performs data conversions in
these situations.
• Assignment — Assignment operations cause some implicit type conversions. This makes
arithmetic operations easier to write. Assigning an integer type variable to a floating type
variable causes an automatic conversion from the integer type to the floating type.
• Function call — Arguments to functions are implicitly converted following a number of
'widening' conversions. For example, characters are automatically converted to integers
when passed as function arguments in the absence of a prototype.
• Normal conversions — In preparation for arithmetic or logical operations, the compiler
automatically converts from one type to another. Also, if two operands are not of the same
type, one or both may be converted to a common type before the operation is performed.
• Casting — You can explicitly force a conversion from one type to another using a cast
operation.
• Returned values — Values returned from a function are automatically converted to the
function's type. For example, if a function was declared to return a double and the return
statement has an integer expression, the integer value is automatically converted to a
double.
Conversions from one type to another do not always cause an actual physical change in
representation. Converting a 16-bit short int into a 64-bit double causes a representational
change. Converting a 16-bit signed short int to a 16-bit unsigned short int does not cause a
representational change.