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Rounding Floating-Point Numbers

Problem

You need to round a floating-point number to an integer.

Solution

Use one of the procedures round, ceiling, floor and truncate.

(floor -4.3)     ==>  -5.0
(ceiling -4.3)   ==>  -4.0
(truncate -4.3)  ==>  -4.0
(round -4.3)     ==>  -4.0
     
(floor 3.5)      ==>  3.0
(ceiling 3.5)    ==>  4.0
(truncate 3.5)   ==>  3.0
(round 3.5)      ==>  4.0  ; inexact
     
(round 7/2)      ==>  4    ; exact
(round 7)        ==>  7

Discussion

The procedures all return integers.

The procedure round returns the closest integer to x, rounding to even when x is halfway between two integers.

The procedure floor returns the largest integer not larger than =x.

The procedure ceiling returns the smalles integer not smaller than x.

The procedure truncate returns the integer closest to x whose absolute value is not larger than the absolute value of x.

If the number given to one of the procedures is inexact?, then the result will also be inexact.

-- ChandraQuintas - 27 Apr 2004 -- JensAxelSoegaard - 10 May 2004