Weird result when multiplying a number with a comma in it

tSpark wrote: I know how to get around this, but I thought it was really odd and wonder if anyone can explain it. <cfoutput>#replace('$1,000','$','','all')*100#</cfoutput> ... By the way, someone donated $1,000 to a charity through this system and was actually charged $42,735!

$42735 - that is $1 for every single day that ever existed on the ColdFusion calendar, up until December 31, 2016. That is because, in essence, the *100 part is making your code to cast the string '1,000' to the date 31st December 2016. In fact, '1,000' is then cast to the number of days since ColdFusion's zero date, 30th December 1899.

Thus,

  <cfoutput>#'1,000' + 0#</cfoutput>

results in 42735, which is the same as

  <cfoutput>#datediff('d', createdate(1899,12,30), createdate(2016,12,31))#</cfoutput>

Similarly, '2,000'+0 is cast to the total number of days until the end of the first month. That is, until 31st January 2017. '3,000' + 0 is cast to the total number of days until the end of the second month. that is, until 28th February 2017. '4,000' + 0 is cast to the total number of days until the third month, that is, until 31st March 2017. And so on.

Another example:

'5,000' + 0: <cfoutput>#'5,000' + 0#</cfoutput><br>

datediff:  <cfoutput>#datediff('d', createdate(1899,12,30), createdate(2017,4,30))#</cfoutput>

Both will give you 42855. Weird but true. The moral here is to be careful when using ambiguous values in a weakly-typed language like ColdFusion.

That's a generous donation! I would have expected an error as well. That is strange.

Funnier, 8,000 and 1,8,000 also calculate into similar numbers and 0,000 throws a cannot parse into a number error -- the expected result of all the examples.