Editing Befunge (section)

== Sample Befunge-93 code ==
The technique of using arrows to change control flow is demonstrated in the random number generator program below.  The Befunge instruction pointer begins in the upper left corner and will travel to the right if not redirected.  Following the arrows around, the <code>?</code> instructions send the instruction pointer in random cardinal directions until the pointer hits a digit, pushing it to the stack. Then the arrows navigate to the <code>.</code> to output the digit from the stack and return the pointer to the first directional randomiser. There is no <code>@</code> to terminate this program, so it produces an endless stream of random numbers from 1 to 9.
<syntaxhighlight lang="befunge">
 v>>>>>v
  12345
  ^?^
 > ? ?^
  v?v
  6789
  >>>> v
 ^    .<
</syntaxhighlight>
The following code is an example of the classic [[Hello world program|"Hello World!" program]]. First the letters "olleH" are pushed onto the stack as [[ASCII]] numbers. These are then popped from the stack in [[LIFO (computing)|LIFO]] order and output as text characters to give "Hello". A space is character number 32 in ASCII, which here is constructed by multiplying 4 and 8, before being output as text. The remaining code then outputs "World!" in a similar way, followed by ASCII character 10 (a [[line feed]] character, moving the output cursor to a new line).
<syntaxhighlight lang="befunge">
>              v
v  ,,,,,"Hello"<
>48*,          v
v,,,,,,"World!"<
>25*,@
</syntaxhighlight>
The following code is a slightly more complicated version. It adds the ASCII character 10 (a [[line feed]] character) to the stack, and then pushes "!dlrow ,olleH" to the stack. Again, [[LIFO (computing)|LIFO]] ordering means that "H" is now the top of the stack and will be the first printed, "e" is second, and so on. To print the characters, the program enters a [[Control flow#Loops|loop]] that first duplicates the top value on the stack (so now the stack would look like "[[line feed|\n]]!dlrow ,olleHH"). Then the "_" operation will pop the duplicated value, and go right if it's a zero, left otherwise. (This assumes a compliant interpreter that "returns" 0 when popping an empty stack.) When it goes left, it pops and prints the top value as an [[ASCII]] character. It then duplicates the next character and loops back to the "_" test, continuing to print the rest of the stack until it is empty and so the next value popped is 0, at which point "@" ends the program.
<syntaxhighlight lang="befunge">
 >25*"!dlrow ,olleH":v
                  v:,_@
                  >  ^
</syntaxhighlight>