# Program for Binary To Decimal Conversion

• Difficulty Level : Easy
• Last Updated : 20 Jun, 2022

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

Examples :

```Input : 111
Output : 7

Input : 1010
Output : 10

Input: 100001
Output: 33```

The idea is to extract the digits of a given binary number starting from the rightmost digit and keep a variable dec_value. At the time of extracting digits from the binary number, multiply the digit with the proper base (Power of 2) and add it to the variable dec_value. In the end, the variable dec_value will store the required decimal number.
For Example:
If the binary number is 111.
dec_value = 1*(2^2) + 1*(2^1) + 1*(2^0) = 7

The below diagram explains how to convert ( 1010 ) to equivalent decimal value: Below is the implementation of the above idea :

## C++

 `// C++ program to convert binary to decimal``#include ``using` `namespace` `std;` `// Function to convert binary to decimal``int` `binaryToDecimal(``int` `n)``{``    ``int` `num = n;``    ``int` `dec_value = 0;` `    ``// Initializing base value to 1, i.e 2^0``    ``int` `base = 1;` `    ``int` `temp = num;``    ``while` `(temp) {``        ``int` `last_digit = temp % 10;``        ``temp = temp / 10;` `        ``dec_value += last_digit * base;` `        ``base = base * 2;``    ``}` `    ``return` `dec_value;``}` `// Driver program to test above function``int` `main()``{``    ``int` `num = 10101001;` `    ``cout << binaryToDecimal(num) << endl;``}`

## Java

 `// Java program to convert``// binary to decimal` `// Function to convert``// binary to decimal``class` `GFG {``    ``static` `int` `binaryToDecimal(``int` `n)``    ``{``        ``int` `num = n;``        ``int` `dec_value = ``0``;` `        ``// Initializing base``        ``// value to 1, i.e 2^0``        ``int` `base = ``1``;` `        ``int` `temp = num;``        ``while` `(temp > ``0``) {``            ``int` `last_digit = temp % ``10``;``            ``temp = temp / ``10``;` `            ``dec_value += last_digit * base;` `            ``base = base * ``2``;``        ``}` `        ``return` `dec_value;``    ``}` `    ``// Driver Code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `num = ``10101001``;``        ``System.out.println(binaryToDecimal(num));``    ``}``}` `// This code is contributed by mits.`

## Python3

 `# Python3 program to convert``# binary to decimal` `# Function to convert``# binary to decimal``def` `binaryToDecimal(n):``    ``num ``=` `n;``    ``dec_value ``=` `0``;``    ` `    ``# Initializing base``    ``# value to 1, i.e 2 ^ 0``    ``base ``=` `1``;``    ` `    ``temp ``=` `num;``    ``while``(temp):``        ``last_digit ``=` `temp ``%` `10``;``        ``temp ``=` `int``(temp ``/` `10``);``        ` `        ``dec_value ``+``=` `last_digit ``*` `base;``        ``base ``=` `base ``*` `2``;``    ``return` `dec_value;` `# Driver Code``num ``=` `10101001``;``print``(binaryToDecimal(num));` `# This code is contributed by mits`

## C#

 `// C# program to convert``// binary to decimal` `// Function to convert``// binary to decimal``class` `GFG {``    ``public` `static` `int` `binaryToDecimal(``int` `n)``    ``{``        ``int` `num = n;``        ``int` `dec_value = 0;` `        ``// Initializing base1``        ``// value to 1, i.e 2^0``        ``int` `base1 = 1;` `        ``int` `temp = num;``        ``while` `(temp > 0) {``            ``int` `last_digit = temp % 10;``            ``temp = temp / 10;` `            ``dec_value += last_digit * base1;` `            ``base1 = base1 * 2;``        ``}` `        ``return` `dec_value;``    ``}` `    ``// Driver Code``    ``public` `static` `void` `Main()``    ``{``        ``int` `num = 10101001;` `        ``System.Console.Write(binaryToDecimal(num));``    ``}``}` `// This code is contributed by mits.`

## PHP

 ``

## Javascript

 ``

Output:

`169`

Time complexity : O( logn)

Auxiliary Space : O(1)

Note: The program works only with binary numbers in the range of integers. In case you want to work with long binary numbers like 20 bits or 30 bit, you can use a string variable to store the binary numbers.

Below is a similar program which uses string variable instead of integers to store binary value:

## C++

 `// C++ program to convert binary to decimal``// when input is represented as binary string.``#include ``#include ``using` `namespace` `std;` `// Function to convert binary to decimal``int` `binaryToDecimal(string n)``{``    ``string num = n;``    ``int` `dec_value = 0;` `    ``// Initializing base value to 1, i.e 2^0``    ``int` `base = 1;` `    ``int` `len = num.length();``    ``for` `(``int` `i = len - 1; i >= 0; i--) {``        ``if` `(num[i] == ``'1'``)``            ``dec_value += base;``        ``base = base * 2;``    ``}` `    ``return` `dec_value;``}` `// Driver program to test above function``int` `main()``{``    ``string num = ``"10101001"``;``    ``cout << binaryToDecimal(num) << endl;``}`

## Java

 `// Java program to convert binary to``// decimal when input is represented``// as binary string.``import` `java.io.*;` `class` `GFG {` `    ``// Function to convert binary to decimal``    ``static` `int` `binaryToDecimal(String n)``    ``{``        ``String num = n;``        ``int` `dec_value = ``0``;` `        ``// Initializing base value to 1,``        ``// i.e 2^0``        ``int` `base = ``1``;` `        ``int` `len = num.length();``        ``for` `(``int` `i = len - ``1``; i >= ``0``; i--) {``            ``if` `(num.charAt(i) == ``'1'``)``                ``dec_value += base;``            ``base = base * ``2``;``        ``}` `        ``return` `dec_value;``    ``}` `    ``// Driver program to test above function``    ``public` `static` `void` `main(String[] args)``    ``{``        ``String num = ``new` `String(``"10101001"``);``        ``System.out.println(binaryToDecimal(num));``    ``}``}` `// This code is contribute by Prerna Saini`

## Python3

 `# Python3 program to convert binary``# to decimal when input is``# represented as binary string.` `# Function to convert``# binary to decimal``def` `binaryToDecimal(n):``    ``num ``=` `n;``    ``dec_value ``=` `0``;``    ` `    ``# Initializing base``    ``# value to 1, i.e 2 ^ 0``    ``base1 ``=` `1``;``    ` `    ``len1 ``=` `len``(num);``    ``for` `i ``in` `range``(len1 ``-` `1``, ``-``1``, ``-``1``):``        ``if` `(num[i] ``=``=` `'1'``):    ``            ``dec_value ``+``=` `base1;``        ``base1 ``=` `base1 ``*` `2``;``    ` `    ``return` `dec_value;` `# Driver Code``num ``=` `"10101001"``;``print``(binaryToDecimal(num));` `# This code is contributed by mits`

## C#

 `// C# program to convert binary to``// decimal when input is represented``// as binary string.``using` `System;` `class` `GFG {` `    ``// Function to convert binary to decimal``    ``static` `int` `binaryToDecimal(String n)``    ``{``        ``String num = n;``        ``int` `dec_value = 0;` `        ``// Initializing base value to 1,``        ``// i.e 2^0``        ``int` `base1 = 1;` `        ``int` `len = num.Length;``        ``for` `(``int` `i = len - 1; i >= 0; i--) {``            ``if` `(num[i] == ``'1'``)``                ``dec_value += base1;``            ``base1 = base1 * 2;``        ``}` `        ``return` `dec_value;``    ``}` `    ``// Driver Code``    ``public` `static` `void` `Main()``    ``{``        ``String num = ``"10101001"``;``        ``Console.WriteLine(binaryToDecimal(num));``    ``}``}` `// This code is contribute by mits`

## PHP

 `= 0; ``\$i``--)``    ``{``        ``if` `(``\$num``[``\$i``] == ``'1'``)    ``            ``\$dec_value` `+= ``\$base``;``        ``\$base` `= ``\$base` `* 2;``    ``}``    ` `    ``return` `\$dec_value``;``}` `// Driver Code``\$num` `= ``"10101001"``;``echo` `binaryToDecimal(``\$num``), ``"\n"``;` `// This code is contributed by aj_36``?>`

## Javascript

 ``

Output :

`169`

Time complexity : O(n) where n is the length of the string.

Auxiliary Space : O(1)

Using pre-defined function:

## C++

 `#include ``using` `namespace` `std;` `int` `main()``{``    ``char` `binaryNumber[] = ``"1001"``;``    ` `    ``cout << stoi(binaryNumber, 0, 2);` `    ``return` `0;``}``// This code is contributed by whysodarkbro`

## C

 `#include ``#include ``#include ` `int` `main()``{``    ``char` `binaryNumber[] = ``"1001"``;``    ``int` `bin, dec = 0;``    ` `    ``bin = ``atoi``(binaryNumber);` `    ``for``(``int` `i = 0; bin; i++, bin /= 10)``        ``if` `(bin % 10)``            ``dec += ``pow``(2, i);` `    ``printf``(``"%d"``, dec);` `    ``return` `0;``}` `// This code is contributed by whysodarkbro`

## Java

 `public` `class` `GFG {``    ``public` `static` `void` `main(String args[])``    ``{``        ``String binaryNumber = ``"1001"``;``        ``System.out.println(Integer.parseInt(binaryNumber, ``2``));``    ``}``}` `// This code is contributed``// By Yash Kumar Arora`

## Python3

 `n ``=` `input``()` `# Convert n to base 2``s ``=` `int``(n, ``2``)` `print``(s)`

## C#

 `using` `System;` `class` `GFG {``    ` `public` `static` `void` `Main()``{``    ``int` `value = 1001;``    ``Console.Write(Convert.ToInt32(value.ToString(), 2));``}``}` `// This code is contributed by SoumikMondal`

## Javascript

 ``

Output :

`9`

Time complexity: O(n) where n is the length of the given string.

Auxiliary Space: O(1)
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