Question

I have a query about data type promotion rules in C language standard.
The C99 says that:

C integer promotions also require that “if an int can represent all values of the original type, the value is converted to an int; otherwise, it is converted to an unsigned int.”

My questions is in case of a C language expression where unsigned int and signed int are present, which type will be promoted to what type?

E.g. int cannot represent all the values of the unsigned int (values larger than MAX_INT values) whereas unsigned int cannot represent the -ve values, so what type is promoted to what in such cases?

Answer 1

I think the following answers your question:

6.3.1.3 Signed and unsigned integers

1 When a value with integer type is
converted to another integer type
other than _Bool, if the value can be
represented by the new type, it is
unchanged.

2 Otherwise, if the new
type is unsigned, the value is
converted by repeatedly adding or
subtracting one more than the maximum
value that can be represented in the
new type until the value is in the
range of the new type.

3 Otherwise,
the new type is signed and the value
cannot be represented in it; either
the result is implementation-defined
or an implementation-defined signal is
raised.