FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)? 
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 FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

This message is one of several periodic postings to comp.lang.perl.misc
intended to make it easier for perl programmers to find answers to
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+
  Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

    The infinite set that a mathematician thinks of as the real numbers can
    only be approximated on a computer, since the computer only has a finite
    number of bits to store an infinite number of, um, numbers.

    Internally, your computer represents floating-point numbers in binary.
    Floating-point numbers read in from a file or appearing as literals in
    your program are converted from their decimal floating-point
    representation (eg, 19.95) to an internal binary representation.

    However, 19.95 can't be precisely represented as a binary floating-point
    number, just like 1/3 can't be exactly represented as a decimal
    floating-point number. The computer's binary representation of 19.95,
    therefore, isn't exactly 19.95.

    When a floating-point number gets printed, the binary floating-point
    representation is converted back to decimal. These decimal numbers are
    displayed in either the format you specify with printf(), or the current
    output format for numbers. (See the section on "$#" in the perlvar
    manpage if you use print. "$#" has a different default value in Perl5
    than it did in Perl4. Changing "$#" yourself is deprecated.)

    This affects all computer languages that represent decimal
    floating-point numbers in binary, not just Perl. Perl provides
    arbitrary-precision decimal numbers with the Math::BigFloat module (part
    of the standard Perl distribution), but mathematical operations are
    consequently slower.

    To get rid of the superfluous digits, just use a format (eg,
    "printf("%.2f", 19.95)") to get the required precision. See the section
    on "Floating-point Arithmetic" in the perlop manpage.

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                                                           04.01
--
    This space intentionally left blank



Tue, 11 May 2004 02:17:01 GMT  
 
 [ 1 post ] 

 Relevant Pages 

1. FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

2. FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

3. FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

4. FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

5. FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

6. FAQ: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

7. FAQ 4.1 Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

8. FAQ 4.1 Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

9. FAQ 4.1 Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

10. FAQ 4.1 Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

11. FAQ 4.1: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

12. FAQ 4.1: Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?

 

 
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