Program for Decimal to Binary Conversion

Given a decimal number as input, we need to write a program to convert the given decimal number into an equivalent binary number.

Examples of Decimal to Binary:

 
Input : 7
Output : 111
Input : 10
Output : 1010
Input: 33
Output: 100001

Brute force Approach

For Example: 
If the decimal number is 10. 
Step 1: Remainder when 10 is divided by 2 is zero. Therefore, arr[0] = 0. 
Step 2: Divide 10 by 2. New number is 10/2 = 5. 
Step 3: Remainder when 5 is divided by 2 is 1. Therefore, arr[1] = 1. 
Step 4: Divide 5 by 2. New number is 5/2 = 2. 
Step 5: Remainder when 2 is divided by 2 is zero. Therefore, arr[2] = 0. 
Step 6: Divide 2 by 2. New number is 2/2 = 1. 
Step 7: Remainder when 1 is divided by 2 is 1. Therefore, arr[3] = 1. 
Step 8: Divide 1 by 2. New number is 1/2 = 0. 
Step 9: Since number becomes = 0. Print the array in reverse order. Therefore the equivalent binary number is 1010.

The below diagram shows an example of converting the decimal number 17 to an equivalent binary number. 

Below is the implementation of the above idea.  

C++

// C++ program to convert a decimal
// number to binary number

#include <iostream>
using namespace std;

// function to convert decimal to binary
void decToBinary(int n)
{
    // array to store binary number
    int binaryNum[32];

    // counter for binary array
    int i = 0;
    while (n > 0) {

        // storing remainder in binary array
        binaryNum[i] = n % 2;
        n = n / 2;
        i++;
    }

    // printing binary array in reverse order
    for (int j = i - 1; j >= 0; j--)
        cout << binaryNum[j];
}

// Driver program to test above function
int main()
{
    int n = 17;
    decToBinary(n);
    return 0;
}

C

// C Code to convert Decimal number into Binary

#include <stdio.h>

void decToBinary(int n)
{
    // array to store binary number
    int binaryNum[32];

    // counter for binary array
    int i = 0;
    while (n > 0) {
        // storing remainder in binary array
        binaryNum[i] = n % 2;
        n = n / 2;
        i++;
    }

    // printing binary array in reverse order
    for (int j = i - 1; j >= 0; j--)
        printf("%d", binaryNum[j]);
}

// Driver program to test above function
int main()
{
    int n = 17;
    decToBinary(n);
    return 0;
}

Java

// Java program to convert a decimal
// number to binary number
import java.io.*;

class GFG {
    // function to convert decimal to binary
    static void decToBinary(int n)
    {
        // array to store binary number
        int[] binaryNum = new int[32];

        // counter for binary array
        int i = 0;
        while (n > 0) {
            // storing remainder in binary array
            binaryNum[i] = n % 2;
            n = n / 2;
            i++;
        }

        // printing binary array in reverse order
        for (int j = i - 1; j >= 0; j--)
            System.out.print(binaryNum[j]);
    }

    // driver program
    public static void main(String[] args)
    {
        int n = 17;
        decToBinary(n);
    }
}

// Contributed by Pramod Kumar

Python3

# Python3 program to convert a
# decimal number to binary number

# function to convert
# decimal to binary
def decToBinary(n):

    # array to store
    # binary number
    binaryNum = [0] * n;

    # counter for binary array
    i = 0;
    while (n > 0):

        # storing remainder
        # in binary array
        binaryNum[i] = n % 2;
        n = int(n / 2);
        i += 1;

    # printing binary array
    # in reverse order
    for j in range(i - 1, -1, -1):
        print(binaryNum[j], end = "");

# Driver Code
n = 17;
decToBinary(n);

# This code is contributed by mits

C#

// C# program to convert a decimal
// number to binary number
using System;

public class GFG {

    // function to convert decimal
    // to binary
    static void decToBinary(int n)
    {
        // array to store binary number
        int[] binaryNum = new int[32];

        // counter for binary array
        int i = 0;
        while (n > 0) {
            // storing remainder in
            // binary array
            binaryNum[i] = n % 2;
            n = n / 2;
            i++;
        }

        // printing binary array
        // in reverse order
        for (int j = i - 1; j >= 0; j--)
            Console.Write(binaryNum[j]);
    }

    // Driver Code
    public static void Main()
    {
        int n = 17;
        decToBinary(n);
    }
}

// This code is contributed by Sam007.

Javascript

<script>

// Javascript program to convert a decimal
// number to binary number

// function to convert decimal to binary
function decToBinary(n)
{
    // array to store binary number
    let binaryNum = new Array(32);

    // counter for binary array
    let i = 0;
    while (n > 0) {

        // storing remainder in binary array
        binaryNum[i] = n % 2;
        n = Math.floor(n / 2);
        i++;
    }

    // printing binary array in reverse order
    for (let j = i - 1; j >= 0; j--)
        document.write(binaryNum[j]);
}

// Driver program to test above function
    let n = 17;
    decToBinary(n);

// This code is contributed by Mayank Tyagi

</script>

PHP

<?php
// PHP program to convert a decimal
// number to binary number

// function to convert
// decimal to binary
function decToBinary($n)
{
    // array to store
    // binary number
    $binaryNum;

    // counter for binary array
    $i = 0;
    while ($n > 0)
    {

        // storing remainder
        // in binary array
        $binaryNum[$i] = $n % 2;
        $n = (int)($n / 2);
        $i++;
    }

    // printing binary array
    // in reverse order
    for ($j = $i - 1; $j >= 0; $j--)
        echo $binaryNum[$j];
}

// Driver Code
$n = 17;
decToBinary($n);

// This code is contributed by m_kit
?>

Output

10001

Time complexity: O(logn) & Auxiliary Space: O(1)

We can use bitwise operators to do the above job. Note that bitwise operators work faster than arithmetic operators used above.

C++

// CPP program to Decimal to binary conversion
// using bitwise operator
// Size of an integer is assumed to be 32 bits
#include <iostream>
using namespace std;

// Function that convert Decimal to binary
void decToBinary(int n)
{
    // Size of an integer is assumed to be 32 bits
    for (int i = 31; i >= 0; i--) {
        int k = n >> i;
        if (k & 1)
            cout << "1";
        else
            cout << "0";
    }
}

// driver code
int main()
{
    int n = 32;
    decToBinary(n);
}

C

// C language to convert Decimal to binary number
// using bitwise operator
// Size of an integer is assumed to be 32 bits

#include <stdio.h>

// Function that convert Decimal to binary
int decToBinary(int n)
{
    // Size of an integer is assumed to be 32 bits
    for (int i = 31; i >= 0; i--) {
        int k = n >> i; // right shift
        if (k & 1) // helps us know the state of first bit
              printf("1");
        else printf("0");
    }
}

// driver code
int main()
{
    int n = 32;
    decToBinary(n);
}

Java

// Java program to Decimal to binary conversion
// using bitwise operator
// Size of an integer is assumed to be 32 bits

class gfg {
    // Function that convert Decimal to binary
    public void decToBinary(int n)
    {
        // Size of an integer is assumed to be 32 bits
        for (int i = 31; i >= 0; i--) {
            int k = n >> i;
            if ((k & 1) > 0)
                System.out.print("1");
            else
                System.out.print("0");
        }
    }
}

class geek {
    // driver code
    public static void main(String[] args)
    {
        gfg g = new gfg();
        int n = 32;
        g.decToBinary(n);
    }
}
// This code is contributed by mits

Python3

# Python3 program to Decimal
# to binary conversion using
# bitwise operator

# Size of an integer is
# assumed to be 32 bits

# Function that convert
# Decimal to binary


def decToBinary(n):

    # Size of an integer is
    # assumed to be 32 bits
    for i in range(31, -1, -1):
        k = n >> i
        if (k & 1):
            print("1", end="")
        else:
            print("0", end="")


# Driver Code
n = 32
decToBinary(n)

# This code is contributed by mits

C#

// C# program to Decimal to binary conversion
// using bitwise operator
// Size of an integer is assumed to be 32 bits
using System;
class gfg {
    // Function that convert Decimal to binary
    public void decToBinary(int n)
    {
        // Size of an integer is assumed to be 32 bits
        for (int i = 31; i >= 0; i--) {
            int k = n >> i;
            if ((k & 1) > 0)
                Console.Write("1");
            else
                Console.Write("0");
        }
    }
}

class geek {
    // driver code
    public static int Main()
    {
        gfg g = new gfg();
        int n = 32;
        g.decToBinary(n);
        return 0;
    }
}

Javascript

<script>

// javascript program to Decimal to binary conversion
// using bitwise operator
// Size of an integer is assumed to be 32 bits


    // Function that convert Decimal to binary
    function decToBinary(n)
    {
        // Size of an integer is assumed to be 32 bits
        for (i = 31; i >= 0; i--) {
            var k = n >> i;
            if ((k & 1) > 0)
                document.write("1");
            else
                document.write("0");
        }
    }

    // driver code
    var n = 32;
    decToBinary(n);

// This code contributed by Princi Singh

</script>

PHP

<?php
// PHP program to Decimal to binary conversion
// using bitwise operator

// Size of an integer is assumed
// to be 32 bits

// Function that convert Decimal to binary
function decToBinary($n)
{

    // Size of an integer is
    // assumed to be 32 bits
    for ( $i = 31; $i >= 0; $i--)
    {
        $k = $n >> $i;
        if ($k & 1)
            echo "1";
        else
            echo "0";
    }
}

    // Driver Code
    $n = 32;
    decToBinary($n);

// This code is contributed by aj_36
?>

Output

00000000000000000000000000100000

Time complexity: O(1) 

loop iterates constant(32) number of times everytime even for small number 

Auxiliary Space: O(1)

Efficient Approach

It’s another efficient approach to converting Decimal to binary using the right shift(>>) and And(&) operator. Here we’ll use only Binary Operators which usually are very fast in computation.

C++

#include <bits/stdc++.h>
using namespace std;

string DecimalToBinary(int num)
{
    string str;
      while(num){
      if(num & 1) // 1
        str+='1';
      else // 0
        str+='0';
      num>>=1; // Right Shift by 1
    }
      return str;
}

void reverse(string str)
{
  for(int i=str.size()-1 ; i>=0 ; i--)
   cout<< str[i];
}

int main() {
    int num = 59;
    cout<< "Binary of num 59 is: ";
      reverse( DecimalToBinary(num) );
    return 0;
}

Java

// Java program to implement the
// above approach
import java.io.*;

class GFG
{

  // the converts decimal to binary base
  static String DecimalToBinary(int num)
  {
    String str = "";
    while (num > 0) {
      if ((num & 1) == 1) // 1
        str += '1';
      else // 0
        str += '0';
      num >>= 1; // Right Shift by 1
    }
    return str;
  }

  // reverse the string
  static void reverse(String str)
  {
    for (int i = str.length() - 1; i >= 0; i--)
      System.out.print(str.charAt(i));
  }
  public static void main(String[] args)
  {
    int num = 59;
    System.out.print("Binary of num 59 is: ");
    reverse(DecimalToBinary(num));
  }
}

// This code is contributed by phasing17

Python3

# Python3 program to implement the above approach
# function to convert the decimal number
# to binary number
def DecimalToBinary(num):
    strs = ""
    while num:
        # if (num & 1) = 1
        if (num & 1):
            strs += "1"
        # if (num & 1) = 0
        else:
            strs += "0"
        # right shift by 1
        num >>= 1
    return strs

# function to reverse the string
def reverse(strs):
    print(strs[::-1])

# Driver Code
num = 59
print("Binary of num 59 is:", end=" ")
reverse(DecimalToBinary(num))

# This code is contributed by phasing17

C#

// C# program to implement the
// above approach

using System;

public class GFG
{

    // this converts decimal to binary base
    public static string DecimalToBinary(int num)
    {
        string str = "";
        while (num > 0) {
            if ((num & 1) == 1) // 1
                str += '1';
            else // 0
                str += '0';
            num >>= 1; // Right Shift by 1
        }
        return str;
    }
    // reverse the string
    public static void reverse(String str)
    {
        for (int i = str.Length - 1; i >= 0; i--)
            Console.Write(str[i]);
    }
    // Driver Code
    public static void Main(string[] args)
    {
        int num = 59;
        Console.Write("Binary of num 59 is: ");
        reverse(DecimalToBinary(num));
    }
}

// this code was contributed by phasing17

Javascript

<script>
// JavaScript program to implement the approach
// function to convert decimal to binary
function DecimalToBinary(num)
{
    var str = "";
    while (num)
    {

        // adding the result of num & 1 to str
        if (num & 1) // 1
            str += '1';
        else // 0
            str += '0';

        // Right Shift by 1
        num >>= 1;
    }
    return str;
}

// function to print reverse of str
function reverse(str)
{
    var res = "";
    for (var i = str.length - 1; i >= 0; i--)
        res += (str[i]);
    document.write(res);
}

// Driver Code
var num = 59;
document.write("Binary of num " + num + " is: ");

// function call
reverse(DecimalToBinary(num));

// This code is contributed by phasing17
</script>

Output

Binary of num 59 is: 111011

Time Complexity:  O(log n) & Auxiliary Space: O(1)

Decimal to binary conversion can also be done without using arrays. 

C++

// C++ implementation of the approach
#include <cmath>
#include <iostream>
using namespace std;

#define ull unsigned long long int

// Function to return the binary
// equivalent of decimal value N
int decimalToBinary(int N)
{
    // To store the binary number
    ull B_Number = 0;
    int cnt = 0;
    while (N != 0) {
        int rem = N % 2;
        ull c = pow(10, cnt);
        B_Number += rem * c;
        N /= 2;
        // Count used to store exponent value
        cnt++;
    }
    return B_Number;
}

// Driver code
int main()
{
    int N = 17;
    cout << decimalToBinary(N);
    return 0;
}

// This code is contributed by Sania Kumari Gupta (kriSania804)

C

// C implementation of the approach
#include <math.h>
#include <stdio.h>

#define ull unsigned long long int

// Function to return the binary
// equivalent of decimal value N
int decimalToBinary(int N)
{
    // To store the binary number
    ull B_Number = 0;
    int cnt = 0;
    while (N != 0) {
        int rem = N % 2;
        ull c = pow(10, cnt);
        B_Number += rem * c;
        N /= 2;
        // Count used to store exponent value
        cnt++;
    }
    return B_Number;
}

// Driver code
int main()
{
    int N = 17;
    printf("%u", decimalToBinary(N));
    return 0;
}

// This code is contributed by Sania Kumari Gupta (kriSania804)

Java

// Java implementation of the approach
import java.io.*;

class GFG
{

// Function to return the binary
// equivalent of decimal value N
static int decimalToBinary(int N)
{

    // To store the binary number
    int B_Number = 0;
    int cnt = 0;
    while (N != 0)
    {
        int rem = N % 2;
        double c = Math.pow(10, cnt);
        B_Number += rem * c;
        N /= 2;

        // Count used to store exponent value
        cnt++;
    }

    return B_Number;
}

// Driver code
public static void main (String[] args)
{

    int N = 17;
    System.out.println (decimalToBinary(N));

}
}

// This code is contributed by ajit.

Python3

# Python3 implementation of the approach

# Function to return the binary
# equivalent of decimal value N
def decimalToBinary(N):

    # To store the binary number
    B_Number = 0
    cnt = 0
    while (N != 0):
        rem = N % 2
        c = pow(10, cnt)
        B_Number += rem * c
        N //= 2

        # Count used to store exponent value
        cnt += 1

    return B_Number

# Driver code
N = 17
print(decimalToBinary(N))

# This code is contributed by
# SHUBHAMSINGH10

C#

// C# implementation of the approach
using System;

class GFG
{

// Function to return the binary
// equivalent of decimal value N
static int decimalToBinary(int N)
{

    // To store the binary number
    int B_Number = 0;
    int cnt = 0;
    while (N != 0)
    {
        int rem = N % 2;
        int c = (int)Math.Pow(10, cnt);
        B_Number += rem * c;
        N /= 2;

        // Count used to store exponent value
        cnt++;
    }

    return B_Number;
}

// Driver code
static public void Main ()
{
    int N = 17;
    Console.Write(decimalToBinary(N));
}
}

// This code is contributed by Tushil.

Javascript

<script>

// javascript implementation of the approach

// Function to return the binary
// equivalent of decimal value N
function decimalToBinary(N)
{

    // To store the binary number
    var B_Number = 0;
    var cnt = 0;
    while (N != 0)
    {
        var rem = N % 2;
        var c = Math.pow(10, cnt);
        B_Number += rem * c;
        N = parseInt(N/2);

        // Count used to store exponent value
        cnt++;
    }
    return B_Number;
}

// Driver code
var N = 17;
document.write(decimalToBinary(N));

// This code is contributed by Princi Singh
</script>

Output

10001

Time complexity: O(logn) & Auxiliary Space: O(1)

Note that this method is similar to the one where we convert Binary to Decimal as discussed in this post.
There is yet another method that converts any Decimal Number to its Binary form. The idea is to use bitset.

Below is the implementation of the above approach. 

C++

//C++ program to convert a decimal number
//to its binary form.

//including header file
#include <bits/stdc++.h>
using namespace std;

//Function to convert a decimal number
//to its binary form
string decimalToBinary(int n)
{
    //finding the binary form of the number and
    //converting it to string.
    string s = bitset<64> (n).to_string();

    //Finding the first occurrence of "1"
    //to strip off the leading zeroes.
    const auto loc1 = s.find('1');

    if(loc1 != string::npos)
        return s.substr(loc1);

    return "0";
}

//Driver Code
int main()
{
    int n = 17;

    //Function call
    cout << decimalToBinary(n);

    return 0;
}

//This code is contributed by yashbeersingh42

Java

// Java program to convert a decimal number to its binary
// form
import java.util.*;

class DecimalToBinary {

  // Function to convert a decimal number to its binary
  // form
  public static String decimalToBinary(int n)
  {

    // Finding the binary form of the number and
    // converting it to a string
    String s = Integer.toBinaryString(n);

    // Finding the first occurrence of "1" to strip off
    // the leading zeroes
    int loc1 = s.indexOf("1");

    if (loc1 != -1) {
      return s.substring(loc1);
    }
    return "0";
  }

  // Driver code
  public static void main(String[] args)
  {
    int n = 17;

    // Function call
    System.out.println(decimalToBinary(n));
  }
}

// This code is contributed by phasing17

Python3

# Python program to convert a decimal number
# to its binary form.

# Function to convert a decimal number
# to its binary form
def decimalToBinary( n):

    # finding the binary form of the number and
    # converting it to string.
    s = bin(n)[2:]

    # Finding the first occurrence of "1"
    # to strip off the leading zeroes.
    # const auto loc1 = s.find('1');
    loc1 = s[s.index('1'):]


    return loc1;

    return "0";

# Driver Code
n = 17;

# Function call
print(decimalToBinary(n));

C#

// C# program to convert a decimal number
// to its binary form.
using System;

class HelloWorld {

  // Function to convert a decimal number
  // to its binary form
  public static String decimalToBinary(int n)
  {
    // finding the binary form of the number and
    //converting it to string.
    String s = Convert.ToString(n, 2);

    return s;
  }

  static void Main() {

    int n = 17;

    //Function call
    Console.WriteLine(decimalToBinary(n));

  }
}

// The code is contributed by Nidhi goel.

Javascript

// Javascript program to convert a decimal number
// to its binary form.

// Function to convert a decimal number
// to its binary form
function decimalToBinary( n)
{
    // finding the binary form of the number and
    // converting it to string.
    const s = n.toString(2);

    return s;
}

// Driver Code
let n = 17;

// Function call
console.log(decimalToBinary(n));

  // This code is contributed by imruhrbf8.

Output

10001

Time complexity: O(logn) & Auxiliary Space: O(1)

Another Approach

C++

// C++ program to convert Decimal to Binary Number
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // input number
    int number = 15;
    int n = (int)(log2(number));

    // binary output
    // using the inbuilt function
    cout << "the binary number is : "
         << bitset<64>(number).to_string().substr(64 - n
                                                  - 1);
}

// This code is written by phasing17

Java

//To convert Decimal to Binary Number//
import java.util.*;
    public class Main{
        public static void main(String [] args){
            //input//
            int number =15;

            //output//
            System.out.println("the binary number is : "+ Integer.toString(number,2));

            //This code is written by ZEESHAN AHMAD//
        }
    }

Python3

# Python3 program to convert Decimal to Binary Number

# input number
number = 15

# binary output
# using the inbuilt function
print("the binary number is :", bin(number)[2::])

# This code is written by phasing17

C#

// To convert Decimal to Binary Number//
using System;
    class GFG{
        public static void Main(){
            //  input//
            int number =15;

            //output//
            Console.WriteLine("the binary number is : "+ Convert.ToString(number, 2));
        }
    }

// This code is contributed by code_hunt.

Javascript

// JavaScript program to convert Decimal to Binary Number

// input number
var number = 15;

// binary output
// using the inbuilt function
console.log("the binary number is :", number.toString(2));

// This code is written by phasing17

Output

the binary number is : 1111

Time complexity: O(logn) & Auxiliary Space: O(1)