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West Bengal University of technology
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B.Tech
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Computer Representation of Numbers and Computer Arithmetic
In a Computer numbers are represented by binary digits 0 and 1. Computers employ
binary arithmetic for performing operations on numbers. Since it gets cumbersome to
display large numbers in binary form computers usually display them in hexadecimal or
octal or decimal system. All of these number systems are positional systems. In a
positional system a number is represented by a set of symbols. Each of these symbols
denote a particular value depending on its position. The number of symbols used in a
positional system depends on its 'base'. Let us now discuss about various positional
number systems:
Decimal System:
The decimal system uses 10 as its base value and employs ten symbols 0 to 9 in
representing numbers. Let us consider a decimal number 7402 consisting of four
symbols 7,4,0,2. In terms of base 10 it can be expressed as follows.
So each of the symbols from a set of symbols denoting a number is multiplied with
power of the base (10) depending on its position counted from the right. The count
always begins with 0.
In general a decimal number
consisting of
symbols can be
expressed as:
where,
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Similarly, a fractional part of a decimal number can be expressed as
Binary system:
Binary system is the positional system consisting of two symbols i.e. 0,1 and '2' as its
base. Any binary number
actually represents a decimal value given by
where
Consider the binary number 10101. The decimal equivalent of 10101 is given by
Hexadecimal System:
The Hexadecimal system is the positional system consisting of sixteen symbols,
0,1,2...9,A,B,C,D,E,F, and '16' as its base. Here the symbols A denotes 10, B denotes
11 and so on. The decimal equivalent of the given hexadecimal number
is
given by
. For example consider
.
We can convert a binary number directly to a hexadecimal number by grouping the
binary digits, starting from the right, into sets of four and converting each group to its
equivalent hexadecimal digit. If in such a grouping the last set falls short of four binary
digits then do the obvious thing of prefixing it with adequate number of binary digit '0'.
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For example let us find the hexadecimal equivalent of
The vice-versa is also true.
Octal System: The octal system is the positional system that uses 8 as its base and
as its symbol set of size 8. The decimal equivalent of an octal number
is given by
. For
example consider
We can get the octal equivalent of a binary number by grouping the binary digits,
starting from the right, into sets of three binary digits and converting each of these sets
to its octal equivalent. If such a grouping results in a last set having less number of
digits it may be prefixed with adequate number of binary digit 0. As an example the
octal equivalent of
Conversion of decimal system to non-decimal system:
To convert a decimal number to a number of any other system we should consider the
integer and fractional parts separately and follow the following procedure:
Conversion of integer part:
(a) Consider the integer part of a given decimal number and divide it by the base b of
the new number system. The remainder will constitute the rightmost digit of the integer
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part of the new number.
(b) Next divide the quotient again by the base b. The remainder will constitute second
digit from the right in the new system.
Continue this process until we end up with a zero-quotient. The last remainder is the
leftmost digit of the new number.
Conversion of fractional part:
(a) Consider the fractional part of the given decimal number and multiply it with the
base b of the new system. The integral part of the product constitutes the leftmost digit
of the fractional part in the new system.
(b) Now again multiply the fractional part resulting in step (a) by the base b of the new
system. The integral part of the resultant product is the second digit from the left in the
new system.
Repeat the above step until we encounter a zero-fractional part or a duplicate fractional
part. The integer part of this last product will be the rightmost digit of the fractional part
of the new number.
Eg: Convert 54.45 into its binary equivalent.
(a) Consider the integer part i.e. 54 and apply the steps listed under conversion of
integer part i.e.
(b) Conversion of fractional part:
Product integral part Binary number
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