CODEWITHSUNDEEP
batch-file
Kristiaan
Kristiaan

Reputation: 253

Batch programming code explanation needed

I'm trying to understand a batch script I found online , the code is designed to check for the last day of the month and terminate the script if the condition is true.

Heres a copy of the code.

REM @echo off
for /F "tokens=1,2,3 delims=/ " %%a in ('echo %date%') do set day=%%a & set month=%%b & set year=%%c

set /a leap=%year% %% 3
if %leap%==0 (set eom=29) else (set eom=28)

echo 01 03 05 07 08 10 12 | find "%month%" > nul && set eom=31
echo 04 06 09 11 | find "%month%" > nul && set eom=30

rem if %eom%==%day% exit

however I understand the rest of the code all except the following two lines.

set /a leap=%year% %% 3
if %leap%==0 (set eom=29) else (set eom=28)

when I've tried to Echo the contents of the leap variable I keep getting 2, but if I'm honest don't truly understand how it would ever get 0 ?

any advice on this would be helpful.

Upvotes: 0

Views: 73

Answers (2)

Happy Face
Happy Face

Reputation: 1071

%% means modulus, since each leap year is 4 years apart e.g. 2012(leap),2013,2014,2015,2016(2nd leap), if value of a leap year is 0, then value of the last year before another leap year is 4.( Think of an array, [0,1,2,3,5], 0 to 4 is 5 numbers apart). And so, 2016 is another leap year, since its value 4 is the 5th number from 0.

If you still confused why modulo 4? Because the leap year divided by 4 is 0, so as I said before, 0 means a leap year.

Upvotes: 1

ankh-morpork
ankh-morpork

Reputation: 1832

It looks like The %leap% variable is being used to check if a year is a leap year. You only ever get 2 when you echo %leap% because 2015 % 3 will always be 2.

It also seems that the logic for checking if it's a leap year is flawed. A general approach for this is

  1. If the year is evenly divisible by 4, go to step 2. Otherwise, go to step 5.
  2. If the year is evenly divisible by 100, go to step 3. Otherwise, go to step 4.
  3. If the year is evenly divisible by 400, go to step 4. Otherwise, go to step 5.
  4. The year is a leap year (it has 366 days).
  5. The year is not a leap year (it has 365 days).

source

Upvotes: 0

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