Integral and floating-point promotions

The integral and floating-point promotions are used automatically as part of the usual arithmetic conversions and default argument promotions. The integral and floating-point promotions do not change either the sign or the magnitude of the value. For more information about the usual arithmetic conversions, see Usual arithmetic conversions.

Integral promotion rules for wchar_t

If a value is of the wchar_t type, the type of the value can be converted to the first of the following types that can represent all the values of the underlying type of wchar_t:

int
unsigned int
long int
unsigned long int
long long int
unsigned long long int

If none of the types in the list can represent all the values of the underlying type of wchar_t, the wchar_t type is converted to the underlying type of wchar_t.

Integral promotion rules for bit field

The rules apply to the following conditions:

The -qupconv option is in effect.
The type of an integral bit field is unsigned.
The type of the integral bit field is smaller than the int type.

If all these conditions are satisfied, one of the following rules applies to the promotion of the integral bit field:

If the unsigned int type can represent all the values of the integral bit field, the bit field is converted to unsigned int.
Otherwise, no integral promotion applies to the bit field.

If any of these conditions is not satisfied, one of the following rules applies to the promotion of the integral bit field:

If the int type can represent all the values of the integral bit field, the bit field is converted to int.
Otherwise, if the unsigned int type can represent all the values, the bit field is converted to unsigned int.
Otherwise, no integral promotion applies to the bit field.

One of the following rules applies to an integral bit field promotion:

If the int type can represent all the values of an integral bit field, the bit field is converted to int.
Otherwise, if the unsigned int type can represent all the values, the bit field is converted to unsigned int.
Otherwise, no integral promotion applies to the bit field.

Integral promotion rules for Boolean

Begin C only If the -qupconv option is in effect, a Boolean value is converted to the unsigned int type with its value unchanged. Otherwise, if the -qnoupconv option is in effect, a Boolean value is converted to the int type with its value unchanged. C only

C++ only If a Boolean value is false, it is converted to an int with a value of 0. If a Boolean value is true, it is converted to an int with a value of 1.

Integral promotion rules for other types

The rules apply to the following conditions:

The -qupconv option is in effect.
The type of an integer type other than bit field and Boolean is unsigned.
The type of the integer type is smaller than the int type.

If all these conditions are satisfied, the integer type is converted to the unsigned int type.

If any of these conditions is not satisfied, one of the following rules applies to the promotion of the integer type:

If the integer type can be represented by the int type and its rank is lower than the rank of int, the integer type is converted to the int type.
Otherwise, the integer type is converted to the unsigned int type.

One of the following rules applies to the promotion of an integer type other than wchar_t, bit field, and Boolean:

If the integer type can be represented by the int type and its rank is lower than the rank of int, the integer type is converted to the int type.
Otherwise, the integer type is converted to the unsigned int type.

floating-point promotion rules

The float type can be converted to the double type. The float value is not changed after the promotion.