note BrowserUk <blockquote><i>if I multiply 0.29 with 50, I get 14.5: Only with this line: my $num4 = sprintf ("%.64f", $num7); I get the exact result in "double" (14.999...). </i></blockquote> <p>The only difference between:<code> print 0.29 * 50;; 14.5 </code> <p>And:<code> printf "%.20f\n", 0.29 * 50;; 14.49999999999999800000 </code> <p>is what gets printed out; not what is calculated and stored internally. <P>All floating point calculations are done internally using IEEE754 semantics; if you want to see the full internal results use [printf] to display the results. <p>As for your perceived difference when gratuitously using eval:<code> printf "%.20f\n", eval eval( 0.29 ) * eval( 50 );; 14.50000000000000000000 </code> <p>The first thing to note is that the first two [eval]s make no difference whatsoever:<code> printf "%.20f\n", eval 0.29 * 50;; 14.50000000000000000000 </code> <P>And the reason for that difference is because (in this form) [eval] expects a string. So the result of the multiplication (<c>eval( 0.29 ) * eval( 50 )</c>) is converted to a string -- using the same rules as [print] -- before being passed to the final [eval]. <p>You get identically different results if you do:<code> $n = 0.29 * 50; printf "%.20f\n", "$n";; 14.50000000000000000000 </code> <P>Because the internal (IEEE754) representation has been lost by the conversion to a string. <P>Bottom line: Stop worrying about it. Do your floating point math in the usual way (no [eval]'s; no stringifications), secure in the full IEEE754 semantics will be used internally; and then use [printf]/[sprintf] (*only*) when you need to display them. <div class="pmsig"><div class="pmsig-171588"> <hr /> <font size=1 > <div>With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'</div> <div>Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.</div> <div>"Science is about questioning the status quo. Questioning authority". </div> <div>In the absence of evidence, opinion is indistinguishable from prejudice. </div> </font> </div></div> 1016160 1016160