Integer

• Supported by hardware.
• Include Short Integer, Integer, Long Integer, Unsigned Integer.
• Sign-magnitude notation vs. Twos complement  (to store a negative number)

Sign-magnitude notation:  the sign bit is set to indicate negative
                                       and the remainder of the bit string represents
                                       the absolute value of the number.
                                       It does not lend itself to computer arithmetic.
Twos complement:  taking the logical complement of the positive version of the number
                              and adding one.  It is conveniert for addition and subtraction.
                              How do you add 7 and -3?
-3₁₀=complement of (00000011)₂ + 1=(11111100+1)₂=11111101₂
                    00000111
                  + 11111101
                   100000100  Take away overflow and get 100₂=4₁₀
Ones complement:  taking the logical complement of its absolute value.
                              It has two representations of zeros.

Floating-Point

• Approximations of real values
• e.g. pi ->3.14   e      1275.33333……
• Scientific notation (factor & exponent)

See Figure 6.1
• Float – 4 bytes
• Double – bigger fraction part, more precise.
• Floating Points Representation

Decimal

• Supported by COBOL
• Fixed numbers of decimal digits.
• Waste of memory but accurate in defined range.

• True and False
• In C: 0 = false,   else = true

• ASCII 128 different characters 8 bit
• Unicode 16-bit character set  (Java was the first to use it).