Basically, we use only 128 total character which is used mostly during program.
But total number of Character in ASCII table is 256 (0 to 255).
0 to 31(total 32 character ) is called as ASCII control characters (character code 0-31).
32 to 127 character is called as ASCII printable characters (character code 32-127).
128 to 255 is called as The extended ASCII codes (character code 128-255).
check reference: http://www.ascii-code.com/
Most of the extended ASCII character isn’t present in the QWERTY (ENGLISH) keyboard, so this is the reason, author took 128 total character in that example in “Cracking the coding interview” book.