How do I use mathematical operators like modulo in Brainf**k?

Question

In BF, I know you can add and subtract with the

+

and

-

operators, and that you can multiply two pre-defined numbers like so:

Multiply 4 and 4

++++[>++++<-]

But how can I multiply two variables, or use other mathematical operators, such as modulo or division?

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Answer 1

Here is a generic looking routine to multiply two numbers in bf. Taken from here.

Multiply a value by another value This requires multiple copies and nested loops.

Copy first operand to a work location
Move to work location and enter a loop
Move to second operand and copy to a work location
Move to second work location and enter a loop
Move to result location and increment
Move to second work location and decrement
Loop until second work location equals zero
Move to first work location and decrement
Loop until first work location equals zero

Example:

Multiply three (a[p]) times five (a[p+1]) and place the result in a[p+2].

+++>+++++< 
[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<
[<<
  [>>>+>+<<<<-]>>>>[<<<<+>>>>-]<
  [<<+>>-]
<-]

Some further reading here

How do I use mathematical operators like modulo in Brainf**k?

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