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Round off

To round off, use sprintf function. Specify the format like "%.3g" or "%.5g" if you want to round off by specifying a valid digit, and "%.3f" or "%." If you want to round off by a digit with a decimal point. Specify as 5f ".

# Specify by the number of digits after the decimal point.
sprintf("%.1f", $num1);

# Specified by the number of significant digits.
sprintf("%.1g", $num1);

To round off, use the sprintf function. The format "%.1f" is a format that rounds a floating point number to the first decimal place. The second decimal place is rounded off.

If you want to round off by specifying the number of significant digits, specify as "%.1g". For example, if you format 37.48 with "%.3g", you will get a number of 37.5.

Notes on rounding

my $num2 = 0.725;
my $num2_round = sprintf("%.2f", $num2);

0.725 expressed in numeric literal is not 0.725 internally. Numerical values that are not expressed in binary are always treated as an approximation 0.72499999999999998 (in my environment) due to internal error.

Rounding this to the third decimal place gives 0.724. This is not the expected result.

Rounding by sprintf is incorrect

Rounded by perl (end0tknr kipple)

It was pointed out that rounding by sprintf should not be done.

As you said, you shouldn't use sprintf if you want to round exactly. Rounding with sprintf works in most cases, with the exceptions mentioned above.

If you want to round more accurately, there is a CPAN module called Math::Round::nearest.

Thank you for pointing out, end0tknr.

Example program

This is an example for rounding.

use strict;
use warnings;

my $num1 = 100.47;

print "(1) Round off.\n";
my $num1_round = sprintf("%.1f", $num1);
print "Rounding $num1 to the second decimal place gives ${num1_round}.\n\n";

print "(2) Notes on rounding\n";
my $num2 = 0.725;

# It does not become 0.73.
my $num2_round = sprintf("%.2f", $num2);
print "If you round 0.725 to the third decimal place, you get ${num2_round}\n\n";

printf("caused internally by the number%.30f\n". $Num2);