Round a number to a specific decimal place

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Implementations[edit]

C[edit]

#include <stdlib.h>
/* Don't forget to free()! the result after using it.
   This code actually truncates instead of rounding values */
char* format(double Value, int nPrecision)
{
   char *buffer = malloc(128*sizeof(char)); //Buffer where to store the resulting formatted string.
   snprintf(buffer,127,"%0.*f",nPrecision,Value); //Print formatted data to a string
   return buffer;
}

For example:

format( 3456.67953, 1 ) results in 3456.6
format( 3456.67953, 2 ) results in 3456.67
format( 3456.67953, 3 ) results in 3456.679

Original source: Ancient Dragon

Common Lisp[edit]

(defun round-to (number precision &optional (what #'round))
    (let ((div (expt 10 precision)))
         (/ (funcall what (* number div)) div)))

The optional parameter "what" can be one of

#'floor
#'ceil
#'truncate
#'round ;;No need to, though.

For example:

* (round-to 1234.4567 0)
1234
* (round-to 1234.4567 1)
2469/2
* (float *)
1234.5
* (round-to -1234.4567 2 #'floor)
-61723/50
* (float *)
-1234.46
* (round-to 1234.4567 3 #'truncate)
154307/125
* (float *)
1234.456

Erlang[edit]

round(Number, Precision) ->
    P = math:pow(10, Precision),
    round(Number * P) / P.

OCaml[edit]

# open Printf;;
# printf "%0.*f";;
- : int -> float -> unit = <fun>

For example:

# printf "%0.*f\n" 1 1234.5678;;
1234.6
- : unit = ()

Perl[edit]

print sprintf "%0.*f", 2, 3456.67953;

PHP[edit]

<?php
echo round(3.4);         // 3
echo round(3.5);         // 4
echo round(3.6);         // 4
echo round(3.6, 0);      // 4
echo round(1.95583, 2);  // 1.96
echo round(1241757, -3); // 1242000
echo round(5.045, 2);    // 5.05
echo round(5.055, 2);    // 5.06
?>

Original source: PHP Manual

Python[edit]

print round(3.4)         # 3
print round(3.5)         # 4
print round(3.6)         # 4
print round(3.6, 0)      # 4
print round(1.95583, 2)  # 1.96
print round(1241757, -3) # 1242000
print round(5.045, 2)    # 5.05
print round(5.055, 2)    # 5.06

Ruby[edit]

class Float
  def round_to(x)
    (self * 10**x).round.to_f / 10**x
  end

  def ceil_to(x)
    (self * 10**x).ceil.to_f / 10**x
  end

  def floor_to(x)
    (self * 10**x).floor.to_f / 10**x
  end
end

For example:

num = 138.249
num.round_to(2)
# => 138.25
num.floor_to(2)
# => 138.24
num.round_to(-1)
# => 140.0

Original source: rbates

Note: Since Ruby 1.9, rounding can be achieved with: [1]

num.round(precision) # 1.23456.round(4) == 1.2346

Zsh[edit]

printf "%.0f\n" 1234567.899