c++ Algorithm to convert an integer into an array of bool

Question

I'm trying to code an algorithm that will save to file as binary strings every integer in a range. Eg, for the range 0 to 7:

Note that the leading zeros and spaces between digits are essential.

What I cant figure out how to do in a simple way is to convert the integers to binary numbers represented by bool []s (or some alternate approach).

EDIT

As requested, my solution so far is:

const int NUM_INPUTS = 6;
bool digits[NUM_INPUTS] = {0};
int NUM_PATTERNS = pow(2, NUM_INPUTS);

for(int q = 0; q < NUM_PATTERNS; q++)
{
    for(int w = NUM_INPUTS -1 ; w > -1 ; w--)
    {

        if( ! ((q+1) % ( (int) pow(2, w)))  )
            digits[w] = !digits[w];

        outf << digits[w] << " ";
    }

    outf << "\n";
}

Unfortunately, this is a bit screwy as the first pattern it gives me is 000001 instead of 000000.

This is not homework. I'm just coding a simple algorithm to give me an input file for training a neural network.

I think you want to do some base conversion instead. Google C++ base 2 — Blender
– Blender, Commented Apr 4, 2012 at 15:01
Binary data is not the same as an array of bools... are you supposed to create your own binary representation of numbers too? — Kiril
– Kiril, Commented Apr 4, 2012 at 15:02
@Shahbaz this isn't homework. I just need a program to automatically generate an input file for a neural network. — Matt Munson
– Matt Munson, Commented Apr 4, 2012 at 15:34

Robᵩ · Accepted Answer · 2012-04-04 16:26:42Z

4

Don't use pow. Just use binary math:

const int NUM_INPUTS = 6;
int NUM_PATTERNS = 1 << NUM_INPUTS;

for(int q = 0; q < NUM_PATTERNS; q++)
{
    for(int w = NUM_INPUTS -1 ; w > -1; w--)
    {
        outf << ((q>>w) & 1) << " ";
    }
    outf << "\n";
}

edited Apr 4, 2012 at 16:26

answered Apr 4, 2012 at 16:13

Robᵩ

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2 Comments

Matt Munson Over a year ago

How does 1 << 6 = 64? I'm not familiar with the << or >> operators.

Robᵩ Over a year ago

x << n shifts the value x to the left by n bits. If you prefer, it doubles the value x, n times. 1, in binary, is "0000_0001". 1 Shifted left 6 times is "0100_0000". In base 10, that is 64. Similarly x >> n shifts the value x to the right by n bits (or halves x, n times). en.wikipedia.org/wiki/Bitwise_operation#Bit_shifts

Shahbaz · Accepted Answer · 2012-04-04 15:04:05Z

3

Note: I'm not providing code, but merely a hint because the question sounds like homework

This is quite easy. See this example:

number = 23
binary representation = 10111
first  digit = (number   )&1 = 1
second digit = (number>>1)&1 = 1
third  digit = (number>>2)&1 = 1
fourth digit = (number>>3)&1 = 1
fifth  digit = (number>>4)&1 = 1

Alternatively written:

temp = number
for i from 0 to digits_count
    digit i = temp&1
    temp >>= 1

Note that the order of digits taken by this algorithm is the reverse of what you want to print.

answered Apr 4, 2012 at 15:04

Shahbaz

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3 Comments

std''OrgnlDave Over a year ago

int compare = 1L << (digits_count - 1); digit i = (temp & compare ? 1 : 0); temp <<= 1;

std''OrgnlDave Over a year ago

In case you're wondering, that'll let you take the digits in the order you wanted...

Shahbaz Over a year ago

@OrgnlDave, I wasn't wondering, it was obvious. I only intend to give the OP a hint though, and let him tackle with the problem himself.

Éric Malenfant · Accepted Answer · 2012-04-04 23:03:52Z

1

The lazy way would be to use std::bitset.

Example:

#include <bitset> 
#include <iostream>

int main()
{
  for (unsigned int i = 0; i != 8; ++i){
    std::bitset<3> b(i);
    std::cout << b << std::endl;
  }
}

If you want to output the bits individually, space-separated, replace std::cout << b << std::endl; with a call to something like Write(b), with Write defined as:

template<std::size_t S>
void Write(const std::bitset<S>& B)
{
  for (int i = S - 1; i >= 0; --i){
    std::cout << std::noboolalpha << B[i] << " ";
  }
  std::cout << std::endl;
}

edited Apr 4, 2012 at 23:03

answered Apr 4, 2012 at 17:00

Éric Malenfant

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1 Comment

Éric Malenfant Over a year ago

@MattMunson: Now that I have access to a real computer with a real screen and a real keyboard, I added an example.

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