In this C program, we have to convert the given **Binary** number into **Decimal**. Converting a Binary number into a Decimal using the C program is very simple. A Binary number is a number that is represented by only **Zeros** and **Ones**. So we need to convert these Zeros and Ones to a number characterized by a Zero to Nine Decimal system. Binary numbers have the **Base of 2** where the Decimal numbers are of the **base 10**.

The Binary number system is essential in Computers, which can only read Binary numbers, called Machine Language. Binary numbers are represented by subscript **2**, and Decimals are represented by subscript **10**.

In this c program, we are using a **Mod** operator inside a '`while loop`

' to convert the **Binary** into **Decimal**. First, we calculate the Remainder using the **Mod**, and we add '**dec**' with **Remainder * Base**, the Base is initialized to** 1**. Divide the number by **10** to remove the last digit, and finally, we multiply Base with **2** to get the output. Let's take a simple example to understand more about this.

1. Let '**0010**' be the Binary number. Take the numbers from the right sides as the powers of** 2**, which means from the right.

0 - 2^0 1 - 2^1 0 - 2^3

Multiply each digit of the Binary number starting from the last with the powers of **2** respectively, Then add all the multiplied digits we get **2** as a decimal digit.

The main logic of this program is to Initialize the variable '**dec=0**' and '**base=1**'. Then read the Binary number into '**num**' and copy it into '**bnum**'. Using a '`while loop`

' with the condition **'num>0**', calculate the Remainder by using the **mod **operator. Then find the Decimal by **num=num/10** and **base=base*2**. Repeat the loop, and display the Binary number as** bnum** and decimal equivalent as **dec**.

**STEP 1:** Include the Header files to use the built-in functions in the C program.

**STEP 2:** Declare the Integer varables '**num**', '**bnum**', '**dec=0**', '**base=1**' and '**rem**'.

**STEP 3:** Read a Binary number from the user and store it into **bnum **and **num**.

**STEP 4:** By using a '`while loop`

' with the condition **num>0,** do step 5

**STEP 5:** **rem=num** and find **dec=dec+rem*base**

**STEP 6:** **num = num / 10** , **base = base * 2**;

**STEP 7: **Repeat step 4

**STEP 8:** Display the Binary number as **bnum**.

**STEP 9:** Display its Decimal equivalent number as '**dec**'.

` ````
#include <stdio.h>
void main() {
int num, bnum, dec = 0, base = 1, rem;
printf("Enter a binary number(1s and 0s)\n");
scanf("%d", & num); /*maximum five digits */
bnum = num;
while (num > 0) {
rem = num%10; /* calculating reminder using mod operator */
dec = dec + rem * base;
num = num / 10; /* finding the decimal */
base = base * 2;
}
printf("The Binary number is = %d\n", bnum);
printf("Its decimal equivalent is =%d\n", dec);
} /* End of main() */
```

Enter a binary number(1s and 0s) 10101 The Binary number is = 10101 Its decimal equivalent is =21