fixed #126

ch04/README.md

@@ -256,13 +256,11 @@ if `grade > 90`, first conditional operator's result is `high pass`. so the fina
 
 ## Exercise 4.25
 
-> What is the value of ~'q' \<< 6 on a machine with 32-bit ints and 8 bit chars, that uses Latin-1 character set in which 'q' has the bit pattern 01110001?
+> What is the value of `~'q' << 6` on a machine with 32-bit `int`s and 8 bit `char`s, that uses Latin-1 character set in which '`q`' has the bit pattern `01110001`?
 
-The final value in decimal representation is `-7296`.
+We see the value of `~ 'q'` is negative. Left-shifting a negative value has **undefined behaviour**.
 
-The bitwise NOT operator (`~`) yields us the Ones' Complement of `0000 0000 0000 0000 0000 0000 0111 0001`, which is `1111 1111 1111 1111 1111 1111 1000 1110`. The value of `1111 1111 1111 1111 1111 1111 1000 1110` in decimal form is `-114`. This may come as a surprise to some as the unsigned value of said binary sequence is `4294967182`. The most significant bit (the left-most bit, commonly referred to as the sign bit) is however "turned on", or `1`, which signifies a negation operation on that particular bit. The value of that particular bit is then `-2147483648`.
-
-We then shift the bits `6` digits to the left, which yields us `1111 1111 1111 1111 1110 0011 1000 0000`. Overflowing bits were discarded. The decimal representation of the binary sequence is `-7296`.
+check <https://stackoverflow.com/questions/19585507/c-not-bitwise-operator-binary-char-conversion>
 
 ## Exercise 4.26