The statement is sweeping and inaccurate, like many a statement by Mr Schildt. Many people recommend throwing his books away. (Amongst other places, see The Annotated Annotated C Standard, and ACCU Reviews — do an author search on Schildt; see also the Definitive List of C Books on Stack Overflow).
It is implementation defined whether right shifting a negative (necessarily signed) integer shifts zeros or ones into the high order bits. The underlying CPUs (for instance, ARM; see also this class) often have two different underlying instructions — ASR or arithmetic shift right and LSR or logical shift right, of which ASR preserves the sign bit and LSR does not. The compiler writer is allowed to choose either, and may do so for reasons of compatibility, speed or whimsy.
ISO/IEC 9899:2011 §6.5.7 Bitwise shift operators
¶5 The result of E1 >> E2is E1 right-shifted E2 bit positions. If E1 has an unsigned type
or if E1 has a signed type and a nonnegative value, the value of the result is the integral
part of the quotient of E1 / 2E2. If E1 has a signed type and a negative value, the
resulting value is implementation-defined.
