Two arithmetic types are compatible only if they are the same type.
The presence of type specifiers in various combinations for arithmetic types may or may not indicate different types. For example, the type signed int is the same as int, except when used as the types of bit fields; but char, signed char, and unsigned char are different types.
The presence of a type qualifier changes the type. That is, const int is not the same type as int, and therefore the two types are not compatible.