How to Reverse A String in a loop

Question

I am writing a program to do convert a decimal number into binary, using repetitive division. I just can't reverse the final answer (which is variable "x").

num = int(input("Enter a number: "))

    remainder = 0
    while num > 0: 
        remainder = num%2
        num = num//2
        x = str(remainder) 
        #print(reversed(x))
    
        print(x[::-1])

output for num = 19

which is reversed from the actual answer, which is 10011 for decimal 19. Also, how can I bring the answer all in one line, so its not written vertically

You can also directly convert a decimal to a binary number using bin(num) — kinshukdua
– kinshukdua, Commented Oct 17, 2021 at 17:32

Sandsten · Accepted Answer · 2021-10-17 17:39:25Z

2

You are just printing the binary numbers one at a time in the loop, you can't relay reverse when they are printed one after another like that.

You could instead insert the binary elements in a list like this

num = 19

remainder = 0
binary = []
while num > 0: 
    remainder = num%2
    num = num//2
    binary.insert(0,str(remainder))

print("".join(binary))

answered Oct 17, 2021 at 17:39

Sandsten

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Comments

Nicolas Forstner · Accepted Answer · 2021-10-17 17:45:03Z

1

num = int(input("Enter a number: "))

s = ''
remainder = 0
while num > 0:
    remainder = num%2
    num = num//2
    s += str(remainder)

print(s[::-1])

You were reversing individual digits, i.e."1", "0" instead of the whole final string. Obviously, reversing strings with length 1 does not do anything.

Alternatives:

num = int(input("Enter a number: "))

s = ''
while num:
    bit = num & 1
    s += str(bit)
    num >>= 1

print(s[::-1])

Or simply:

print(bin(int(input("Enter a number: "))))

edited Oct 17, 2021 at 17:45

answered Oct 17, 2021 at 17:39

Nicolas Forstner

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Comments

Kesslwovv · Accepted Answer · 2021-10-17 17:38:15Z

0

you can remove the newline after a print by doing:

print(x[::-1], end='')

answered Oct 17, 2021 at 17:38

Kesslwovv

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