# Negative numbers to binary system with Python

## Question:

I’m solving a task using Python.

I need to count the number of non-zero bits in a given value. I don’t have any problems with positive numbers as I use the function bin() and count the number of ‘1’, but can’t understand what’s wrong with negative. In example, -1 is equal to `11111111111111111111111111111111`

, but when I use the function bin() it gives ‘-0b1’. Please, tell me how can I convert it right.

## Answers:

Just need to add 2**32 (or 1 << 32) to the negative value.

```
bin(-1+(1<<32))
'0b11111111111111111111111111111111'
```

or use following command for all the values:

```
a = bin(val if val>0 else val+(1<<32))
```

Use `num % maxnum`

:

```
bin(-1 % 20) == bin(19)
```

The reason you are getting what you have, as explained in the comments, is because of how ints are represented in binary. I would not be able to tell you much, but it has to do with a variety of things including arbitrary byte size, unsigned/signed ints, etc etc.

So to achieve what you want (the int to wrap around some arbitrary max value, in this case 32 bit), just use modulo:

```
bin(num % 2*32)
```

Just a note that the difference between using `%`

versus simply `+`

the max num is that this will work for both positive and negative numbers.