Need help in adding binary numbers in python

Question

If I have 2 numbers in binary form as a string, and I want to add them I will do it digit by digit, from the right most end. So 001 + 010 = 011 But suppose I have to do 001+001, how should I create a code to figure out how to take carry over responses?

What have you tried so far? You should document some of your attempts so the question is not closed prematurely. — jww
– jww, Commented Jan 29, 2014 at 7:25

Mostly Harmless · Accepted Answer · 2014-01-29 01:48:39Z

43

bin and int are very useful here:

a = '001'
b = '011'

c = bin(int(a,2) + int(b,2))
# 0b100

int allows you to specify what base the first argument is in when converting from a string (in this case two), and bin converts a number back to a binary string.

answered Jan 29, 2014 at 1:48

Mostly Harmless

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Comments

HarmonicaMuse · Accepted Answer · 2021-06-21 14:40:36Z

12

This accepts an arbitrary number or arguments:

>>> def bin_add(*bin_nums: str) -> str: 
...     return bin(sum(int(x, 2) for x in bin_nums))[2:]
...
>>> x = bin_add('1', '10', '100')
>>> x
'111'
>>> int(x, base = 2)
7

edited Jun 21, 2021 at 14:40

answered Jul 17, 2015 at 0:28

HarmonicaMuse

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Comments

Algorithmatic · Accepted Answer · 2014-11-16 04:39:39Z

Here's an easy to understand version

def binAdd(s1, s2):
    if not s1 or not s2:
        return ''

    maxlen = max(len(s1), len(s2))

    s1 = s1.zfill(maxlen)
    s2 = s2.zfill(maxlen)

    result  = ''
    carry   = 0

    i = maxlen - 1
    while(i >= 0):
        s = int(s1[i]) + int(s2[i])
        if s == 2: #1+1
            if carry == 0:
                carry = 1
                result = "%s%s" % (result, '0')
            else:
                result = "%s%s" % (result, '1')
        elif s == 1: # 1+0
            if carry == 1:
                result = "%s%s" % (result, '0')
            else:
                result = "%s%s" % (result, '1')
        else: # 0+0
            if carry == 1:
                result = "%s%s" % (result, '1')
                carry = 0   
            else:
                result = "%s%s" % (result, '0') 

        i = i - 1;

    if carry>0:
        result = "%s%s" % (result, '1')
    return result[::-1]

mshsayem · Accepted Answer · 2014-01-29 02:29:08Z

5

Can be simple if you parse the strings by int (shown in the other answer). Here is a kindergarten-school-math way:

>>> def add(x,y):
        maxlen = max(len(x), len(y))

        #Normalize lengths
        x = x.zfill(maxlen)
        y = y.zfill(maxlen)

        result = ''
        carry = 0

        for i in range(maxlen-1, -1, -1):
            r = carry
            r += 1 if x[i] == '1' else 0
            r += 1 if y[i] == '1' else 0

            # r can be 0,1,2,3 (carry + x[i] + y[i])
            # and among these, for r==1 and r==3 you will have result bit = 1
            # for r==2 and r==3 you will have carry = 1

            result = ('1' if r % 2 == 1 else '0') + result
            carry = 0 if r < 2 else 1       

        if carry !=0 : result = '1' + result

        return result.zfill(maxlen)

>>> add('1','111')
'1000'
>>> add('111','111')
'1110'
>>> add('111','1000')
'1111'

edited Jan 29, 2014 at 2:29

answered Jan 29, 2014 at 2:23

mshsayem

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1 Comment

airstrike Over a year ago

thanks -- this is super useful when doing things like adding floats since they may have a bunch of zeroes to the left which get discarded by many other addition methods. I'm sure there are actual libraries to do float addition, but when you're trying to learn how they work, this comes in handy ;-)

user15023244 · Accepted Answer · 2021-06-21 20:08:27Z

1

It works both ways

# as strings
a = "0b001"
b = "0b010"
c = bin(int(a, 2) + int(b, 2))

# as binary numbers
a = 0b001
b = 0b010
c = bin(a + b)

answered Jun 21, 2021 at 20:08

user15023244

Comments

Arturo Morales Rangel · Accepted Answer · 2019-02-28 07:56:18Z

0

you can use this function I did:

def addBinary(self, a, b):
    """
    :type a: str
    :type b: str
    :rtype: str
    """
    #a = int('10110', 2) #(0*2** 0)+(1*2**1)+(1*2**2)+(0*2**3)+(1*2**4) = 22
    #b = int('1011', 2) #(1*2** 0)+(1*2**1)+(0*2**2)+(1*2**3) = 11

    sum = int(a, 2) + int(b, 2)

    if sum == 0: return "0"

    out = []

    while sum > 0:
        res = int(sum) % 2
        out.insert(0, str(res))
        sum = sum/2


    return ''.join(out)

answered Feb 28, 2019 at 7:56

Arturo Morales Rangel

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Comments

kumar gaurav · Accepted Answer · 2022-08-01 13:49:52Z

#addition of two binary string without using 'bin' inbuilt function

numb1 = input('enter the 1st binary number')
numb2 = input("enter the 2nd binary number")
list1 = []
carry = '0'


maxlen = max(len(numb1), len(numb2))
x = numb1.zfill(maxlen)
y = numb2.zfill(maxlen)


for j in range(maxlen-1,-1,-1):
    d1 = x[j]
    d2 = y[j]
    if d1 == '0' and d2 =='0' and carry =='0':
        list1.append('0')
        carry = '0'
    elif d1 == '1' and d2 =='1' and carry =='1':
        list1.append('1')
        carry = '1'
    elif (d1 == '1' and d2 =='0' and carry =='0') or (d1 == '0' and d2 =='1' and 
carry =='0') or (d1 == '0' and d2 =='0' and carry =='1'):
        list1.append('1')
        carry = '0'
    elif d1 == '1' and d2 =='1' and carry =='0':
        list1.append('0')
        carry = '1'
    else:
        list1.append('0')


    
if carry == '1':
    list1.append('1')

addition = ''.join(list1[::-1])
print(addition)

M.A. · Accepted Answer · 2024-06-27 06:25:14Z

0

def addBinary(self, A, B):
        min_len, res, carry, i, j = min(len(A), len(B)), '', 0, len(A) - 1, len(B) - 1
        while i>=0 and j>=0:
            r = carry
            r += 1 if A[i] == '1' else 0
            r += 1 if B[j] == '1' else 0
            res = ('1' if r % 2 == 1 else '0') + res
            carry = 0 if r < 2 else 1
            i -= 1
            j -= 1

        while i>=0:
            r = carry
            r += 1 if A[i] == '1' else 0
            res = ('1' if r % 2 == 1 else '0') + res
            carry = 0 if r < 2 else 1
            i -= 1
        
        while j>=0:
            r = carry
            r += 1 if B[j] == '1' else 0
            res = ('1' if r % 2 == 1 else '0') + res
            carry = 0 if r < 2 else 1
            j -= 1
        if carry == 1:
            return '1' + res
        return res

edited Jun 27, 2024 at 6:25

M.A.

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answered Apr 18, 2022 at 14:37

Chethan Ck

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1 Comment

Cristik Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Sanya · Accepted Answer · 2020-01-07 04:36:16Z

Not an optimal solution but a working one without use of any inbuilt functions.

    # two approaches

    # first - binary to decimal conversion, add and then decimal to binary conversion
    # second - binary addition normally


    # binary addition - optimal approach
    # rules
    # 1 + 0 = 1
    # 1 + 1 = 0 (carry - 1)
    # 1 + 1 + 1(carry) = 1 (carry -1)

    aa = a
    bb = b
    len_a = len(aa) 
    len_b = len(bb) 

    min_len = min(len_a, len_b) 
    carry = 0
    arr = []

    while min_len > 0:
        last_digit_aa = int(aa[len(aa)-1]) 
        last_digit_bb = int(bb[len(bb)-1]) 

        add_digits = last_digit_aa + last_digit_bb + carry
        carry = 0
        if add_digits == 2:
            add_digits = 0
            carry = 1
        if add_digits == 3:
            add_digits = 1
            carry = 1

        arr.append(add_digits) # will rev this at the very end for output
        aa = aa[:-1]
        bb = bb[:-1]
        min_len -= 1

    a_len_after = len(aa)
    b_len_after = len(bb)

    if a_len_after > 0:
        while a_len_after > 0:
            while carry == 1:
                if len(aa) > 0:
                    sum_digit = int(aa[len(aa) - 1]) + carry
                    if sum_digit == 2:
                        sum_digit = 0
                        carry = 1
                        arr.append(sum_digit)
                        aa = aa[:-1]
                    else:
                        carry = 0
                        arr.append(sum_digit)
                        aa = aa[:-1]
                else:
                    arr.append(carry)
                    carry = 0

            if carry == 0 and len(aa) > 0:
                arr.append(aa[len(aa) - 1])
                aa = aa[:-1]
            a_len_after -= 1

    if b_len_after > 0:
        while b_len_after > 0:
            while carry == 1:
                if len(bb) > 0:
                    sum_digit = int(bb[len(bb) - 1]) + carry
                    if sum_digit == 2:
                        sum_digit = 0
                        carry = 1
                        arr.append(sum_digit)
                        bb = bb[:-1]
                    else:
                        carry = 0
                        arr.append(sum_digit)
                        bb = bb[:-1]
                else:
                    arr.append(carry)
                    carry = 0

            if carry == 0 and len(bb) > 0:
                arr.append(bb[len(bb) - 1])
                bb = bb[:-1]
            b_len_after -= 1

    if carry == 1:
        arr.append(carry)

    out_arr = reversed(arr)
    out_str = "".join(str(x) for x in out_arr)
    return out_str

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