Java: Multiply two binary numbers

Last update on May 12 2025 13:19:59 (UTC/GMT +8 hours)

Binary Multiplication

Write a Java program to multiply two binary numbers.

In digital electronics and mathematics, 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).

Test Data:
Input first binary number: 110
Input second binary number: 101

Sample Solution:

Java Code:

import java.util.Scanner;
public class Exercise18 {
 public static void main(String[] args) {
  // Declare variables to store two binary numbers and the product
  long binary1, binary2, multiply = 0;
  
  // Initialize digit and factor variables for processing binary2
  int digit, factor = 1;
  
  // Create a Scanner object to read input from the user
  Scanner in = new Scanner(System.in);
  
  // Prompt the user to input the first binary number
  System.out.print("Input the first binary number: ");
  binary1 = in.nextLong();
  
  // Prompt the user to input the second binary number
  System.out.print("Input the second binary number: ");
  binary2 = in.nextLong();
  
  // Process binary2 to calculate the product
  while (binary2 != 0) {
   digit = (int)(binary2 % 10);
   if (digit == 1) {
    binary1 = binary1 * factor;
    multiply = binaryproduct((int) binary1, (int) multiply);
   } else {
    binary1 = binary1 * factor;
   }
   binary2 = binary2 / 10;
   factor = 10;
  }
  
  // Display the product of the two binary numbers
  System.out.print("Product of two binary numbers: " + multiply + "\n");
 }

 // Method to calculate the product of two binary numbers
 static int binaryproduct(int binary1, int binary2) {
  int i = 0, remainder = 0;
  int[] sum = new int[20];
  int binary_prod_result = 0;

  while (binary1 != 0 || binary2 != 0) {
   sum[i++] = (binary1 % 10 + binary2 % 10 + remainder) % 2;
   remainder = (binary1 % 10 + binary2 % 10 + remainder) / 2;
   binary1 = binary1 / 10;
   binary2 = binary2 / 10;
  }

  if (remainder != 0) {
   sum[i++] = remainder;
  }
  
  --i;
  
  while (i >= 0) {
   binary_prod_result = binary_prod_result * 10 + sum[i--];
  }

  return binary_prod_result;
 }
}

Explanation:

In the exercise above -

Initialize variables to store the two binary numbers ('binary1' and 'binary2'), the result 'multiply', and other necessary variables.
Take two binary numbers from the user using the Scanner class.
Next, it enters a loop to perform binary multiplication by considering the digits of the second binary number one by one from right to left.
For each digit in 'binary2', if it's 1, it multiplies 'binary1' by a factor. It computes the product using the "binaryproduct()" function.
The helper function "binaryproduct()" calculates the binary product of two numbers and returns the result.
If the digit in binary2 is 0, it still multiplies 'binary1' by the factor but doesn't perform the product calculation.
It updates 'binary2' by moving to the next digit (right to left) and adjusting the factor.
After the loop, it prints the product of the two binary numbers, which is stored in the multiply variable.

Sample Output:

Input the first binary number: 110                                                                            
Input the second binary number: 101                                                                           
Product of two binary numbers: 11110

Flowchart:

Flowchart: Java exercises: Multiply two binary numbers

Flowchart : binaryproduct()

Flowchart: Java exercises: Multiply two binary numbers

For more Practice: Solve these Related Problems:

Multiply three binary numbers instead of two.
Perform binary multiplication without converting to decimal.
Write a program that multiplies binary numbers of different bit lengths.
Modify the program to multiply a binary number by a decimal number directly.

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