Perform arithmetic in loop with variables in Batch

Question

I would like to print the following:

I have tried this:

ECHO OFF
FOR /L %%A in (1,1,5) DO (
    SET /a "B=%%A-1"
    ECHO %B%
)

However, this gives me:

How can I achieve the desired output while using both A and B in my code?

This is a delayed expansion problem. Too lazy to google it, but there are hundreds of questions like this on SO already. Why not just for /L %%A in (0,1,4)? If that's not practical, then you should setlocal enabledelayedexpansion and echo !B!. For more info, do help set in a cmd console, paying attention to the section beginning "Finally, support for delayed environment variable expansion has been added." — rojo
– rojo, Commented Dec 12, 2016 at 18:57
That code does not output a 4 five times. It will output ECHO IS OFF five times. — Squashman
– Squashman, Commented Dec 12, 2016 at 19:06
@Squashman It output ECHO IS OFF five times the first time I ran it, but ouput 4 five times the next time I ran it. — IslandPatrol
– IslandPatrol, Commented Dec 12, 2016 at 19:18
That's because you ran it a second time without closing the cmd prompt (on a related note, good on you for running the script from the command prompt instead of double-clicking it). — SomethingDark
– SomethingDark, Commented Dec 12, 2016 at 19:39

Magoo · Accepted Answer · 2016-12-12 21:48:51Z

8

ECHO OFF
setlocal
FOR /L %%A in (1,1,5) DO (
    SET /a "B=%%A-1"
    call ECHO %%B%%
)

Since you are not using setlocal, B will be set to the value from the previous run. %B% will be replaced by 4 since B was set to 4 by the previous run. the call echo trick uses a parsing quirk to retrieve the current (run-time) value of the variable.

Here's "the official" way:

ECHO OFF
setlocal enabledelayedexpansion
FOR /L %%A in (1,1,5) DO (
    SET /a "B=%%A-1"
    ECHO !B!
)

In delayedexpansion mode, !var! retrieves the value of var as it changes at run-time. This is not without its drawbacks, but you'd need to read up on delayedexpansion for a guide on that matter.

answered Dec 12, 2016 at 21:48

Magoo

80.8k8 gold badges68 silver badges92 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

a_girl Over a year ago

batch is such a pain

Collectives™ on Stack Overflow

Perform arithmetic in loop with variables in Batch

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related