- Write a program in Java to convert binary number to decimal number using Integer.parseInt method.
- Write a function in java to convert binary to decimal numbers.

We have to **convert a binary number**( base 2) **to decimal number** (base 10). Binary number system is a base 2 number system using digits 0 and 1 whereas Decimal number system is base 10 and using digits from 0 to 9. Given a **binary number** as input from user convert it to **decimal number**.

Input Binary Number 0101 Decimal Number 5

## Java program to convert binary to decimal number using parseInt method

In this program, we will use **parseInt** method of Integer class to convert a binary number to decimal number.

**static int parseInt(String s, int radix);**

Above method of Integer class, parses the string argument as a signed integer in the radix specified by the second argument.

**s**: A number represented as a string.**radix**: Base(or Radix) of the input number used to convert String s into integer.

**Arguments**

package com.tcc.java.programs; import java.util.*; public class BinaryToDecimal { public static void main(String args[]) { String binary; Scanner in = new Scanner(System.in); System.out.println("Enter a Binary Number"); binary = in.nextLine(); System.out.println("Decimal Number : "+Integer.parseInt(binary,2)); } }Output

Enter a Binary Number 1001 Decimal Number : 9

## Java program to convert binary to decimal using while loop

**Algorithm to convert Binary to Decimal number**

- We multiply each binary digit with 2
^{i}and add them, where i is the position of the binary digit(starting from 0) from right side. Least significant digit is at position 0.

Let's convert 0101 binary number to decimal number

Decimal number = 0*2^{3}+ 1*2^{2}+ 0*2^{1}+ 1*2^{0}= 0 + 4 + 0 + 1 = 5

package com.tcc.java.programs; import java.util.*; public class BinaryToDecimalTwo { public static void main(String args[]) { int num, decimal = 0, i=0; Scanner in = new Scanner(System.in); System.out.println("Enter a Binary Number"); String binary = in.nextLine(); num = Integer.parseInt(binary); while(num != 0){ decimal += (num%10)*Math.pow(2, i); num = num /10; i++; } System.out.println("Decimal Number : "+ decimal); } }Output

Enter a Binary Number 100 Decimal Number : 4

Enter a Binary Number 10101 Decimal Number : 21