Calculating Ranges of Data Types in C

Question

I\'m working through K&R Second Edition, and can\'t figure out why I\'m getting a certain result. The problem I\'m solving is calculating upper and lower limits for data

Answer 1

Output:

1. Note:
   “In the expression i >>= 1, a negative value is shifted right. The C standard says this is an implementation-defined operation, and many implementations define it to be arithmetic shift. In an arithmetic shift, the most significant bit is unchanged (keeps MSB (signed bit) = 1)".

   (you can read: Right shifting negative numbers in C that >> is compiler dependent whether its singed or unsinfed shift, but probably in your case its doing an Arithmetic Shift.)

   For this reason after code:

    i = ~0;  
    i >>= 1;
   

   i remains ~0. that is in binary == 11111111111111111111111111111111.

   And because ~0 == 11111111111111111111111111111111 is == 2'c complement of 1 that is -1.

   So when you prints with format string %d it print -1. You should use %u to print max unsigned value that is == ~0.

   Important to note here:

   §6.2.6.2 Language 45, ©ISO/IEC ISO/IEC 9899:201x

   (ones’ complement). Which of these applies is implementation-defined, as is whether the value with sign bit 1 and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones’ complement), is a trap representation or a normal value. In the case of sign and magnitude and ones’ complement, if this representation is a normal value it is called a negative zero.

   Your understanding that :

   ~0 >> 1 == 011111111111111111111111111111111 is wrong! (it may be but not happening in your system, according to output)

   ~0 >> 1 == 111111111111111111111111111111111, note MSB(signed bit) is 1.

   For unsigned shift, try following:

   ~0U >> 1 == 011111111111111111111111111111111

   Notice Suffix U for unsigned.

2. Second printf:
   Because i is -1, So in second expression -i - 1 == - (-1) - 1 == 1 - 1 == 0 so output is zero : 0.