Re: Different values while applying format specifiers

Thank you all for the insights. But why does it have to work for 10.1, 3.1 and not 5.1, 4.1

printf("%d\n",100 * 3.1);
print "10.1 Manipulation\n";
printf("%d\n",100 * 10.1);
$c=sprintf("%d\n",100 * 10.1);
printf("%.0f\n",100 * 10.1);
print $c;

print "5.1 Manipulation\n";
printf("%d\n",100 * 5.1);
$d=sprintf("%d\n",100 * 5.1);
printf("%.0f\n",100 * 5.1);
print $d;
[download]

This is the output that I see for the above code

310
10.1 Manipulation
1010
1010
1010
5.1 Manipulation
509
510
509
[download]

Comment on Re: Different values while applying format specifiers Select or Download Code

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Re^2: Different values while applying format specifiers by kennethk (Abbot) on Aug 26, 2014 at 21:47 UTC
To explore what the numbers actually look like in memory, print them out with unrealistic precision: `printf "%.16f\n", 5.1 * 100; printf "%.16f\n", 10.1 * 100; printf "%.16f\n", 20.1 * 100;` [download] And read that link. #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.	[reply] [d/l]
Re^2: Different values while applying format specifiers by pme (Monsignor) on Aug 26, 2014 at 22:05 UTC
Decimal 5.1 is an endless repeating binary number in IEEE-754 format and therefore the value in the memory represents 5.09999999999 in decimal. Accordingly decimal 3.1 is not an endless binary float in the memory.	[reply]
Re^2: Different values while applying format specifiers by Anonymous Monk on Aug 27, 2014 at 11:38 UTC
Just to word pme's response a little more simply: Some decimal numbers can be represented by IEEE-754 exactly, others cannot. For lots more information see the article linked above, or search the Wikipedia page Floating point for the term "exact".	[reply]