CSC322 C Programming and UNIX - Department of Computer ...

Binary Number Representation
C guarantees a base 2 representation for all unsigned integer types:
– Example: 16 bit representation (short on many implementations) of 42
0 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0
2 15
2 14
2 13
2 12
2 11
2 10
2 9
42 = 2 5 + 2 3 + 2 1 = 32 + 8 + 2
– If a result of an arithmetic operation results in a value not representable by the
result type, it is reduced modulo 2 n , where n is the width of the result type
An unsigned number of a narrower type is converted to a wider type by adding
an appropiate number of leading zeroes:
– The 8 bit representation (char on many implementations) of 42 is:
0 0 1 0 1 0 1 0
2 7
2 6
2 5
2 4
2 3
2 2
2 1
2 0
The exact representation for signed integers is not fixed, however, positive signed
integers are guaranteed to have the same representation in signed and unsigned
types
Stephan Schulz 228
2 8
2 7
2 6
2 5
2 4
2 3
2 2
2 1
2 0