Rounding When Last Number is Zero - Applescript - objective-c

Question

I've been using a simple little script for rounding numbers to the hundredths decimal place, however I've noticed that when the number ends in zero, it rounds up to the next decimal place. I need to preserve this decimal place.
For example: 7.49908302 would be rounded to 7.5 instead of 7.50.
How can I keep the hundredths decimal with this subroutine? Should I try something Perl or Objective C, as I've been told Applescript isn't the best for this sort of thing.
Here's the call:
set finalAge514years to (roundThis(age514years, 2))
Here's my rounding subroutine:
on roundThis(n, numDecimals)
set x to 10 ^ numDecimals
(((n * x) + 0.5) div 1) / x
end roundThis

Answer 1

The numbers 7.5 and 7.50 are exactly the same, so Applescript truncates any unnecessary information when displaying the number. What you're really looking for is how to format that information when it is displayed. For that, you need to turn the number into a string, specifying the amount of decimal places you want to see during the conversion.
This method of formatting a number is actually considered one of the Essential sub-routines.
round_truncate(7.49908302, 2)
--> "7.50"
on round_truncate(this_number, decimal_places)
if decimal_places is 0 then
set this_number to this_number + 0.5
return number_to_text(this_number div 1)
end if
set the rounding_value to "5"
repeat decimal_places times
set the rounding_value to "0" & the rounding_value
end repeat
set the rounding_value to ("." & the rounding_value) as number
set this_number to this_number + rounding_value
set the mod_value to "1"
repeat decimal_places - 1 times
set the mod_value to "0" & the mod_value
end repeat
set the mod_value to ("." & the mod_value) as number
set second_part to (this_number mod 1) div the mod_value
if the length of (the second_part as text) is less than the decimal_places then
repeat decimal_places - (the length of (the second_part as text)) times
set second_part to ("0" & second_part) as string
end repeat
end if
set first_part to this_number div 1
set first_part to number_to_string(first_part)
set this_number to (first_part & "." & second_part)
return this_number
end round_truncate
on number_to_string(this_number)
set this_number to this_number as string
if this_number contains "E+" then
set x to the offset of "." in this_number
set y to the offset of "+" in this_number
set z to the offset of "E" in this_number
set the decimal_adjust to characters (y - (length of this_number)) thru ¬
-1 of this_number as string as number
if x is not 0 then
set the first_part to characters 1 thru (x - 1) of this_number as string
else
set the first_part to ""
end if
set the second_part to characters (x + 1) thru (z - 1) of this_number as string
set the converted_number to the first_part
repeat with i from 1 to the decimal_adjust
try
set the converted_number to ¬
the converted_number & character i of the second_part
on error
set the converted_number to the converted_number & "0"
end try
end repeat
return the converted_number
else
return this_number
end if
end number_to_string

Answer 2

You specifically asked for a Perl or Objective-C alternative to Applescript.
Therefore, here is a Perl solution:
use strict;
use warnings;
print round_this(7.49908302, 2), "\n";
sub round_this {
my ($n, $decimals) = #_;
sprintf '%.*f', $decimals, $n;
}
output
7.50

Answer 3

Well AppleScript does many things for you. Because normally 1.5 is not the same as 0.75 * 2 (or at least not stable) in a boolean expression. To make real comparison easy for you the 1.50 (the result of 0.75 * 2) will be coerced into 1.5 for you. To make it work in AppleScript you need a string representation of the real number. However coercing a real into a string, AppleScript will take the system's localization into consideration. So the decimal mark and thousand separator can be different between machines depending on it's system preferences. The rounding is done by AppleScript when coercing a real to an integer. So something like this can work for you:
set n to 7.49958302
set i to round n rounding toward zero
set f to (n - i) * 100 as integer
set f to text 1 thru 2 of (f & "00" as string)
set r to (i as string) & "." & f
When you need this string back to a real again you can easily use the run script command. The run script command is like an eval. In AppleScript code the real numbers are not localized.
run script "7.50"