Prints '+' to the screen 20 times using a loop and arithmetic operators

Question

I have a simple Brainfuck program called "PuraPuraNanya", which prints the character + to the screen 20 times using a loop and arithmetic operators.

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

Here are explanations of what the program does:

• ++++++++++ initializes the value of the current memory cell to 10.
• [ starts a loop.
• >+ moves the value of the current memory cell to the next cell and increments it by 1.
• >+++ moves the value of the current memory cell to the second next cell and increments it by 3.
• >++++ moves the value of the current memory cell to the third next cell and increments it by 4.
• >+++++ moves the value of the current memory cell to the fourth next cell and increments it by 5.
• <<<<- moves the cursor to the first memory cell and decrements its value by 1.
• ] closes the loop.
• >++ moves the cursor to the next memory cell and increments its value by 2.
• . prints the character + to the screen.

I expected the program to print the character + to the screen 20 times. However, when I ran the program, there were no errors and the compiler did not produce the expected output. Can anyone help me check and identify where the mistake is?

Test :

• https://ideone.com/phgfFM - No output
• https://www.jdoodle.com/execute-brainfuck-online/ - Output : dot (.), one time
• https://copy.sh/brainfuck/ - No output

Answer 1

So. The memory starts as all 0s. Before you start the loop, memory is:

10 0 0 0 0 ...

The > commands don't move values as you said, they only move the pointer. Then you increment some cells. So after the first time through the loop, your memory will be:

9 1 3 4 5

with the pointer back at the (just decremented) 9. After the second time through,

8 2 6 8 10

After the 10th iteration of the loop, memory is

0 10 30 40 50

and the loop terminates because you ended at a 0 (at the leftmost cell).

Then you move right one cell and increment twice. This makes a 12:

0 12 30 40 50

Then you output a 12.

Unfortunately, 12 is the ASCII code for "form feed", a control character and not a printable character. What that looks like will depend on your interpreter/compiler.

If you wanted to output a + you would want to output a 43 and not a 12. And if you wanted to output it 20 times you would probably want to use a loop to do that; maybe you want one loop to help build a 20 and a 43, and then another loop to output the 43 20 times while decrementing the 20.

Alternatively, you could just put 43 (+) commands and then 20 (.) commands, and no loops.)