From QB64 Wiki
Revision as of 14:52, 5 March 2021 by Dkearns (talk | contribs) (Fix example highlighting/linking)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

The LOG math function returns the natural logarithm of a specified numerical value.


logarithm! = LOG(value)


  • value MUST be greater than 0. "Illegal function call" error occurs if negative or zero values are used.
  • The natural logarithm is the logarithm to the base e = 2.718282 (approximately).
  • The natural logarithm of a is defined as the integral from 1 to a of dx/x.
  • Returns are default SINGLE precision unless the value parameter uses DOUBLE precision.


Example 1: FUNCTION to find the base ten logarithm of a numerical value.

FUNCTION Log10#(value AS DOUBLE) STATIC Log10# = LOG(value) / LOG(10.#) END FUNCTION

Explanation: The natural logarithm of the value is divided by the base 10 logarithm. The LOG of ten is designated as a DOUBLE precision return by using # after the Log10 value. The return tells you the number of times 10 goes into a value.

Example 2: A binary FUNCTION to convert INTEGER values using LOG to find the number of digits the return will be.

FUNCTION BIN$ (n&) IF n& < 0 THEN EXIT FUNCTION 'positive numbers only! negative error! FOR p% = 0 TO INT(LOG(n& + .1) / LOG(2)) 'added +.1 to get 0 to work IF n& AND 2 ^ p% THEN s$ = "1" + s$ ELSE s$ = "0" + s$ 'find bits on NEXT p% IF s$ = "" THEN BIN$ = "&B0" ELSE BIN$ = "&B" + s$ 'check for zero return END FUNCTION

Explanation: The LOG of a positive INTEGER value is divided by the LOG of 2 to determine the number of binary digits that will be returned. The FOR loop compares the value with the exponents of two and determines if a bit is ON or OFF as "1" or "0".

See also

Keyword Reference - Alphabetical
Keyword Reference - By Usage
Main Wiki Page