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Convert Decimal to Binary in Python

Keep dividing by 2, save the remainders, reverse them. bin(10) is 0b1010 if you are in a hurry.

BeginnerBasic Python ProgramsExample 23 of 25

convert-decimal-to-binary.py

1# Program to convert decimal to binary without using bin()
2
3num = int(input("Enter a non-negative integer: "))
4
5if num < 0:
6    print("Please enter a non-negative integer.")
7elif num == 0:
8    print("Binary: 0")
9else:
10    binary_digits = []
11    n = num
12    while n > 0:
13        remainder = n % 2
14        binary_digits.append(str(remainder))
15        n //= 2
16
17    binary_digits.reverse()
18    binary_str = ''.join(binary_digits)
19    print(f"Binary of {num} is {binary_str}")

Output

Enter a non-negative integer: 10
Binary of 10 is 1010

In this one

remainders come out backwards — reverse them
zero needs a special case or you print a blank

What's going on

10 in binary is 1010. You get there by:

10 / 2 → rem 0

5 / 2 → rem 1

2 / 2 → rem 0

1 / 2 → rem 1

Remainders come out backwards (0101), so reverse. bin(10) is '0b1010'. Writing it by hand is the point.

0 is a special case. The while loop never runs, reverse of empty is empty, and you print nothing. That's why num == 0 is handled first.

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