convert_decimal_to_binary.py

################################################################################
#
# Program: Convert A Decimal Number To A Binary Number
#  
# Description: Program to convert a decimal number to a binary number using 
# Python.  More specifically, this program implements an algorithm to convert a
# non-negative integer to its binary number representation.
#
# YouTube Lesson: https://www.youtube.com/watch?v=B_2Z97sqRQs
#
# Author: Kevin Browne @ https://portfoliocourses.com
#
################################################################################

# Conversion Algorithm:
#
# Repeat until the number is equal to 0:
#
#   Divide the number by 2:
#     - remainder is the next digit in the binary number
#     - quotient is used as the number in next iteration

# For example, converting 43 to binary using this algorithm looks like this:
# 
# 43 / 2 = 21 remainder 1 
# 21 / 2 = 10 remainder 1
# 10 / 2 =  5 remainder 0
#  5 / 2 =  2 remainder 1
#  2 / 2 =  1 remainder 0
#  1 / 2 =  0 remainder 1
#
# Where the remainder of the last division operation becomes the leading digit
# of the binary number, and the remainder of the first division operation 
# becomes the last digit of the binary number.  
#
#       101011-----
#      /  |  \    |
#    32 + 8 + 2 + 1 = 43
#

# Continually prompt the user to enter a valid non-negative integer until they
# do, store the result into decimal
while True:

    # Prompts the user to enter the integer, converts the text entered by the 
    # user and returned by input() from a string to an int value and stores 
    # it into decimal
    decimal = int(input("Enter A Non-Negative Integer: "))

    # If decimal is a negative integer reminder the user the integer must 
    # be non-negative
    if decimal < 0:
        print("Integer Must Be A Non-Negative Integer")
    else:
        # Stops the loop once decimal is a non-negative integer
        break 

# Stores the binary number, represented as a string of 1s and 0s
binary = ""

# Implements the algorithm described above, repeatedly dividing the number by 2
while True:

    # divmod() will return both the quotient and remainder of decimal / 2, we 
    # notably store the quotient back into decimal as we want the quotient of 
    # the previous division operation to become the new decimal number in the 
    # next division operation
    decimal, remainder = divmod(decimal, 2)

    # We essentially "prepend" the next binary number digit onto the front of 
    # the binary number (represented as a string) using the string concatenation
    # operation '+'.  This will build the binary number in the correct order, as
    # noted above the leading digit of the binary number will be the remainder 
    # of the last division operation.
    binary = str(remainder) + binary 

    # Stops the loop/algorithm when the quotient reaches 0
    if decimal == 0:
        break 

# Output the resulting binary number
print(binary)