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units - conversion program
You have: meters
You want: feet
* 3.2808399
/ 0.3048
You have: cm^3
You want: gallons
* 0.00026417205
/ 3785.4118
You have: meters/s
You want: furlongs/fortnight
* 6012.8848
/ 0.00016630952
You have: 1|2 inch
You want: cm
* 1.27
/ 0.78740157
Powers of units can be specified using the '^' character as shown in the example, or by simple concatenation: 'cm3' is equivalent to 'cm^3'. Multiplication of units can be specified by using spaces, a dash or an asterisk. Division of units is indicated by the slash ('/'). Note that multiplication has a higher precedence than division, so 'm/s/s' is the same as 'm/s^2' or 'm/s s'. Division of numbers must be indicated using the vertical bar ('|'). To convert half a meter, you would write '1|2 meter'. If you write '1/2 meter' then the units program would interpret that as equivalent to '0.5/meter'. If you enter incompatible unit types, the units program will print a message indicating that the units are not conformable and it will display the reduced form for each unit:
You have: ergs/hour
You want: fathoms kg^2 / day
conformability error
2.7777778e-11 kg m^2 / sec^3
2.1166667e-05 kg^2 m / sec
The conversion information is read from a units data file. The default file includes definitions for most familiar units, abbreviations and metric prefixes. Some constants of nature included are:
The unit 'pound' is a unit of mass.
Compound names are run together
so 'pound force' is a unit of force.
The unit 'ounce' is also a unit
of mass.
The fluid ounce is 'floz'.
British units that differ from
their US counterparts are prefixed with 'br', and currency is prefixed
with its country name: 'belgiumfranc', 'britainpound'.
When searching
for a unit, if the specified string does not appear exactly as a unit
name, then
will try to remove a trailing 's' or a
trailing 'es' and check again for a match.
To find out what units are available read the standard units file. If you want to add your own units you can supply your own file. A unit is specified on a single line by giving its name and an equivalence. Be careful to define new units in terms of old ones so that a reduction leads to the primitive units which are marked with '!' characters. The program will not detect infinite loops that could be caused by careless unit definitions. Comments in the unit definition file begin with a '/' character at the beginning of a line.
Prefixes are defined in the same was as standard units, but with a trailing dash at the end of the prefix name. If a unit is not found even after removing trailing 's' or 'es', then it will be checked against the list of prefixes. Prefixes will be removed until a legal base unit is identified.
Here is an example of a short units file that defines some basic units.
Exponents entered by the user can be only one digit. You can work around this by multiplying several terms.
The user must use | to indicate division of numbers and / to indicate division of symbols. This distinction should not be necessary.
The program contains various arbitrary limits on the length of the units converted and on the length of the data file.
The program should use a hash table to store units so that it does not take so long to load the units list and check for duplication.
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