Printing a float with a certain number of digits after the decimal point

#1

Hi

Is it possible to print floats with a specified number of digits after the decimal point ?
Suppose number is 3.1425826 and I want only the 2 numbers after the decimal point
so it would print 3.14.
Could this be done using calculations , or another way ?

Any advice is welcome !

Thanks Ronny Suy

#2

A simple way would be to convert the floating-point number to a string:

> (princ-to-string (/ 9 7))
"1.28571"

then use subseq to extract the part you want:

> (subseq (princ-to-string (/ 9 7)) 0 4)
"1.28"

Here’s a slightly better solution that rounds correctly:

(defun dp2 (x)
  (let* ((int (truncate x))
         (dp (round (* 100 (- x int)))))
    (princ int) (princ #\.) (princ dp))
  nothing)

This gives:

>  (dp2 (/ 9 7))
1.29