C Program to Convert Octal to Decimal

Introduction

The base number is used to convert octal to decimal in C, as it is for any other number conversion. To convert an octal number system to a decimal number system, multiply each octal digit by the power of 8, starting on the rightmost digit and multiplying it with 8 to the power zero then move left, for every next digit increase power of 8. Sum up all the products to get the decimal number.

Consider the diagram below to see how to convert octal to decimal.

Algorithm to Convert Octal to Decimal

The concept is to extract the digits of an octal number starting with the rightmost digit and store them in a variable called ans. Multiply the digit with the appropriate base (Power of 8) and add it to the variable ans when extracting digits from an octal number. The variable ans will ultimately hold the requisite decimal number.

Steps: Assume that num is the input octal number.

1. Initialize x = 0, ans = 0.
2. Repeat the following steps while num > 0.
   • Set -> y = num % 10, y will have last digit.
   • Remove last digit of number in num variable -> num = num / 10.
   • ans = ans + y * 8^x
   • updated vale of x varable by 1 till num > 0 -> x = x + 1
3. Return ans.

Program to Convert Octal to Decimal in C

Output:

Explanation:

In OctalToDecimal function, While loop will traverse over the number and extract the digits from it then add the product of the digit and appropriate power of 8 to the ans. In the end, ans will have the converted decimal number which OctalToDecimal() returns.