What does "!" mean in pseudo-code? I know "!" stands for factorial but I can't translate it

!= means not equal and ! generally means not or negation.

It means "not". So your example code

if (operation!= ’B’ OR operation != ’D’ OR operation!= ’W’)

can be read as

"If operation does not equal 'B' or operation does not equal 'D' or operation does not equal 'W'"

In general,

! means not
|| means logical or
&& means logical and

Example:

!false == true  ( == means equality )

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