Decimal to binary in Python.

The program

Press Run to see what it prints. Change anything you like, then run it again.

def to_binary(n):
    if n == 0:
        return "0"
    bits = ""
    while n > 0:
        bits = str(n % 2) + bits
        n = n // 2
    return bits

for number in [5, 10, 25, 100, 255]:
    print(number, "is", to_binary(number), "in binary")
print("Check:", bin(25), int("11001", 2))

5 is 101 in binary
10 is 1010 in binary
25 is 11001 in binary
100 is 1100100 in binary
255 is 11111111 in binary
Check: 0b11001 25

How it works

1. Binary uses only 0 and 1. Each place is worth twice the one to its right: 1, 2, 4, 8, 16, ...
2. To convert, keep dividing by 2. The remainders, read from the last to the first, are the binary digits.
3. Python can do it for you with bin(), and int("11001", 2) turns binary back to a number.

Try this

• Convert your age.
• Write to_decimal to go the other way.
• How many bits does 1000 need?

Stuck on an error? Read how to debug Python.