# Program for Binary To Decimal Conversion

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

Examples:

```Input : 111
Output : 7

Input : 1010
Output : 10

Input: 100001
Output: 33
```

## Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

The idea is to extract the digits of given binary number starting from right most 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. At 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

Below diagram explains how to convert ( 1010 ) to equivalent decimal value:

Below is the C++ implementation of above idea.

```// C++ program to convert binary to decimal
#include<iostream>
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;
}
```

Output:

```169
```

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 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<iostream>
#include<string>
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] == '0')
{
dec_value += 0*base;
base = base * 2;
}
else
{
dec_value += 1*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) == '0')
{
dec_value += 0 * base;
base = base * 2;
}
else
{
dec_value += 1 * 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
```

Output:

```169
```

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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