Java: Convert a binary number to decimal number

Last update on May 12 2025 13:17:53 (UTC/GMT +8 hours)

Binary to Decimal Converter

Write a Java program to convert a binary number to a decimal number.

Binary number: A binary number is a number expressed in the base-2 numeral system or binary numeral system. This system uses only two symbols: typically 1 (one) and 0 (zero).

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.

Pictorial Presentation: Binary to Decimal number

Java: Convert a binary number to decimal number

Sample Solution:

Java Code:

import java.util.Scanner;

public class Exercise22 {
    public static void main(String[] args) {
        // Create a Scanner object to read input from the user
        Scanner sc = new Scanner(System.in);
        
        // Declare variables to store binary and decimal numbers, remainder, and a multiplier
        long binaryNumber, decimalNumber = 0, j = 1, remainder;
        
        // Prompt the user to input a binary number
        System.out.print("Input a binary number: ");
        binaryNumber = sc.nextLong();

        // Convert the binary number to decimal
        while (binaryNumber != 0) {
            remainder = binaryNumber % 10;
            decimalNumber = decimalNumber + remainder * j;
            j = j * 2;
            binaryNumber = binaryNumber / 10;
        }
        
        // Display the decimal representation of the binary number
        System.out.println("Decimal Number: " + decimalNumber);
    }
}

Explanation:

In the exercise above -

It takes a binary number as input from the user using the "Scanner" class and stores it in the variable 'binaryNumber'.
It initializes a variable 'decimalNumber' to store the decimal equivalent and another variable 'j' as a multiplier, starting from 1.
It enters a loop to perform the binary-to-decimal conversion:

In each iteration, it calculates the remainder when the 'binaryNumber' is divided by 10 (which gives the least significant binary digit).
It then adds this remainder multiplied by the current value of 'j' to the 'decimalNumber'.
It multiplies 'j' by 2 to prepare for the next binary digit.
It updates 'binaryNumber' by removing the least significant digit (rightmost) and by dividing it by 10.
The loop continues until 'binaryNumber' becomes zero, effectively converting the entire binary number to decimal.

After the loop, it prints the decimal representation of the binary number stored in the 'decimalNumber' variable.

Sample Output:

Input a binary number: 100                                                                                    
Decimal Number: 4

Flowchart:

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

For more Practice: Solve these Related Problems:

Convert a negative binary number to decimal.
Modify the program to accept binary numbers up to 32 bits.
Write a program to handle binary-to-decimal conversion without using loops.
Implement binary-to-decimal conversion using bitwise operations.

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