Java Program For Decimal to Octal Conversion

Last Updated : 14 Apr, 2025

Given a decimal number N, convert N into an equivalent octal number, i.e., convert the number with base value 10 to base value 8. The decimal number system uses 10 digits from 0-9, and the octal number system uses 8 digits from 0-7 to represent any numeric value.

Illustration: Basic input/output for decimal to octal conversion.

Input : 33
Output: 41
Input : 10
Output: 12

Approach 1:

Store the remainder when the number is divided by 8 in an array. Divide the number by 8 now.
Repeat the above two steps until the number is not equal to 0.
Print the array in reverse order now.

decToOctal — Example of converting the decimal number 33 to an equivalent octal number.

Example:

Java

// Java program to convert a Decimal Number to Octal Number // Importing input output classes import java.io.*; // Main class class Geeks {  // Method  // To convert decimal to octal  static void decToOctal(int n)  {  // Creating an Integer array of  // array to store octal number  int[] octalNum = new int[100];  // counter for octal number array  int i = 0;  while (n != 0) {  // Storing remainder in octal array  octalNum[i] = n % 8;  n = n / 8;  i++;  }  // Printing octal number array in reverse order  for (int j = i - 1; j >= 0; j--)  System.out.print(octalNum[j]);  }  // Method 2  // Main driver method  public static void main(String[] args)  {  // Custom input Integer number  int n = 33;  // Calling the above method to convert  // Decimal to Octal number  decToOctal(n);  } }

Output

Complexity Analysis:

Time complexity: O(log N)
Auxiliary space: O(1) it is using constant space for variable and array OctalNum.

Approach 2:

Initialize ocatalNum with 0 and countVal with 1 and the decimal number as n
Calculate the remainder when the decimal number is divided by 8
Update octal number with octalNum + (remainder * countval)
Increment the countval by countval*10
Divide the decimal number by 8
Repeat from step 2 until the decimal number is zero

Example:

Java

// Java Program to Convert Decimal Number to Octal Number // Importing input output classes import java.io.*; // Main class class Geeks {  // Method 1  // To calculate the octal value of the given  // decimal number  static void decimaltooctal(int deciNum)  {  // Initially declaring and initializing the  // octal number with zero  int octalNum = 0, countval = 1;  int dNo = deciNum;  // Condition check  while (deciNum != 0) {  // Decimals remainder is calculated  int remainder = deciNum % 8;  // Storing the octalvalue  octalNum += remainder * countval;  // Storing exponential value  countval = countval * 10;  deciNum /= 8;  }  // Print and display the octal number  System.out.println(octalNum);  }  // Method 2  // Main driver method  public static void main(String[] args)  {  // Custom input decimal number  int n = 33;  // Calling the Method1 to convert above number  // to Octal number system  decimaltooctal(n);  } }