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Program for Decimal to Binary Conversion

  • Difficulty Level : Easy
  • Last Updated : 22 May, 2022

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

Examples: 

 
Input : 7
Output : 111

Input : 10
Output : 1010

Input: 33
Output: 100001

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;
}

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.

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
?>

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>
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
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;
        if (k & 1)
            cout << "1";
        else
            cout << "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;
    }
}

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
?>

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>
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;
}

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
Output
10001

Time complexity: O(logn) 

Auxiliary Space: O(1) 
Another Approach:

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.
Output
the binary number is : 1111

Time complexity: O(logn) 

Auxiliary Space: O(1) 

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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