Java: Convert a decimal number to octal number

Last update on May 12 2025 13:19:57 (UTC/GMT +8 hours)

Decimal to Octal Converter

Write a Java program to convert a decimal number to an octal number.

Decimal number: The decimal numeral system is the standard system for denoting integer and non-integer numbers. It is also called base-ten positional numeral system.

Octal number: The octal numeral system is the base-8 number system, and uses the digits 0 to 7.

Pictorial Presentation: Decimal to Octal number

Java: Convert a decimal number to octal number

Sample Solution:

Java Code:

import java.util.Scanner;

public class Exercise21 {
    public static void main(String args[]) {
        // Declare variables to store decimal number, remainder, quotient, and an array for octal digits
        int dec_num, rem, quot, i = 1, j;
        int oct_num[] = new int[100];
        
        // Create a Scanner object to read input from the user
        Scanner scan = new Scanner(System.in);

        // Prompt the user to input a decimal number
        System.out.print("Input a Decimal Number: ");
        dec_num = scan.nextInt();

        // Initialize the quotient with the decimal number
        quot = dec_num;

        // Convert the decimal number to octal and store octal digits
        while (quot != 0) {
            oct_num[i++] = quot % 8;
            quot = quot / 8;
        }

        // Display the octal representation of the decimal number
        System.out.print("Octal number is: ");
        for (j = i - 1; j > 0; j--) {
            System.out.print(oct_num[j]);
        }
        
        System.out.print("\n");
    }
}

Explanation:

In the exercise above -

It takes a decimal number ('dec_num') as input from the user using the "Scanner" class.
It initializes an array 'oct_num' to store the octal digits of the converted number and other necessary variables.
It enters a loop to perform the decimal-to-octal conversion:

In each iteration, it calculates the remainder of 'dec_num' when divided by 8 and stores it in the 'oct_num' array.
It then updates 'dec_num' by dividing it by 8 (which effectively shifts it to the right).
The loop continues until 'dec_num' becomes zero, effectively converting the entire decimal number to octal.

After the loop, it prints the octal representation of the decimal number by iterating through the 'oct_num' array in reverse order.

Sample Output:

Input a Decimal Number: 15                                                                                    
Octal number is: 17

Flowchart:

Flowchart: Java exercises: Convert a decimal number to octal number

For more Practice: Solve these Related Problems:

Convert a negative decimal number to octal.
Modify the program to handle decimal numbers with decimal points.
Write a program to display both binary and octal representations of a decimal number.
Implement decimal-to-octal conversion using recursion.

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