Python Program to Convert Octal to Decimal and Vice-Versa – Full Guide

In this article, We make a python program to convert Octal to Decimal and vice-versa. Let’s start.

The octal numeral system, or oct for short, is the base-8 number system and uses the digits 0 to 7. The main characteristic of an Octal Numbering System is that there are only 8 distinct counting digits from 0 to 7 with each digit having a weight or value of just 8 starting from the least significant bit (LSB). 

In the decimal number system, each digit represents the different power of 10 making them base-10 number system.

Problem definition: Convert Octal to Decimal

Create a python program to convert an octal number into a decimal number.

Algorithm

1. Take an octal number as input.
2. Multiply each digit of the octal number starting from the last with the powers of 8 respectively.
3. Add all the multiplied digits.
4. The total sum gives the decimal number.

Program

num = input("Enter an octal number :")

OctalToDecimal(int(num))

def OctalToDecimal(num): 
      
    decimal_value = 0 
    base = 1
  
    while (num): 
        last_digit = num % 10
        num = int(num / 10)
        decimal_value += last_digit * base
        base = base * 8  
    print("The decimal value is :",decimal_value)

Output

Enter an octal number :24
The decimal value is :20

In python, there is an alternate way to convert octal numbers into decimals using the int() method.

Program alternate way

octal_num = input("Enter an octal number :")
decimal_value = int(octal_num,8)
print("The decimal value of {} is {}".format(octal_num,decimal_value))

Output

Enter an octal number :24
The decimal value of 24 is 20

Problem definition: Convert Decimal to Octal

Create a python program to convert a decimal number into an octal number.

Algorithm

1. Take a decimal number as input.
2. Divide the input number by 8 and obtain its remainder and quotient.
3. Repeat step 2 with the quotient obtained until the quotient becomes zero.
4. The resultant is the octal value.

Program

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

print("The octal equivalent is :",decimal_to_octal(decimal))

def decimal_to_octal(decimal):
    octal = 0
    i = 1
    while (decimal != 0):
        octal = octal + (decimal % 8) * i
        decimal = int(decimal / 8)
        i = i * 10
    return octal

Output

Enter a decimal number :200
The octal equivalent is : 310

An alternate shorthand to convert a decimal number into octal is by using the oct() method.

Program alternate way

decimal_number = int(input("Enter a decimal number :"))
octal_number = oct(decimal_number).replace("0o", "")
print("The octal value for {} is {}".format(decimal_number,octal_number ))

Output

Enter a decimal number :200
The octal value for 200 is 310

Recommended read: Check If A Number Is A Perfect Square Or Not