Today we will learn C program to Convert Decimal to Binary and also convert Binary to Decimal number. Before start learning, you should have a little bit of knowledge of Binary and decimal Numbers.

### What is Binary Number?

The Binary Number is number which has base 2. which consists of only two numerical symbols ‘1’ and ‘0’ and each digit is referred to as a ‘Bit’.

**For Example** 5 in binary can be written as 0101.

### What is Decimal Number?

The number which has base 10 is called a Decimal Number system.

**For Example** 0101=**2^3*0+2^2*1+2^1*0+2^0*1**=0+4+0+1=5.

There are so many ways to convert Decimal to binary and vice versa. we will see it one by one.

## 1. Program to Convert decimal to Binary

In this program, we will ask user to enter the number which the users want to convert it into Binary.

**Decimal to Binary Conversion Algorithm:**

**1 Step:** At first divide the number by 2 by using modulus operator ‘%’ and store the remainder in the array.

**2 Step:** divide that number by 2.

**3 Step:** Now repeat the step until the number is greater than 0.

#include <stdio.h> int main() { int a[10], number, i, j; printf("\n Please Enter the Number You want to Convert : "); scanf("%d", &number); for(i = 0; number > 0; i++) { a[i] = number % 2; number = number / 2; } printf("\n Binary Number of a Given Number = "); for(j = i - 1; j >= 0; j--) { printf(" %d ", a[j]); } printf("\n"); return 0; }

**Output:**

**Explanation:**

Let us consider the input number as 5. At first, the value of i is 0.

**1st Iteration:** for(i=0;number>0;i++) i.e (i=0;5>0;0++) conition is true and a[0]=number%2=5%2=1. Therefore,number=number/2=2.5.

**2nd Iteration:** for(i=0;number>0;i++) i.e (i=1;2>0;1++) conition is true and a[1]=number%2=2.5%2=0. Therefore,number=2.5/2=1.25.

**3rd Iteration:** for(i=0;number>0;i++) i.e (i=2;1>0;2++) conition is true and a[2]=number%2=1.25%2=1. Therefore,number=number/2=0.

In this program, we have used for loop.

## 2. C Program to Convert Binary to Decimal

In this program, we will convert the Binary input to Decimal.

**Binary to Decimal Conversion Algorithm:**

**1 Step:** Take a Binary Input to convert into Decimal.

**2 Step:** Multiply each binary digit starting from last with the power of 2 i.e(2^0,2^1).

**3 Step:** make an addition of the multiplied digits.

**4 Step**: Thus the addition gives the Decimal output.

#include <math.h> #include <stdio.h> int convert(long long n); int main() { long long n; printf("Enter a binary number: "); scanf("%lld", &n); printf("%lld in binary = %d in decimal", n, convert(n)); return 0; } int convert(long long n) { int dec = 0, i = 0, rem; while (n != 0) { rem = n % 10; n /= 10; dec += rem * pow(2, i); ++i; } return dec; }

**Output:**

## 3. C program to Convert Decimal to Binary Using While loop

In this program, we have used while loop instead of for loop but the logic behind the conversion is the same.

#include <stdio.h> int main() { int a[10], number, i = 1, j; printf("\n Please Enter the Number You want to Convert : "); scanf("%d", &number); while(number != 0) { a[i++] = number % 2; number = number / 2; } printf("\n Binary Number of a Given Number = "); for(j = i - 1; j > 0; j--) { printf(" %d ", a[j]); } return 0; }

**Output:**

## 4. Decimal to Binary Using Function

In this program, we will use the user-defined function and Bitwise AND operator to convert a decimal number into binary.

#include <stdio.h> void Decimal_to_Binary(int number) { int j; for(int i = 31; i >= 0; i--) { j = number >> i; if(j & 1) printf("1"); else printf("0"); } } int main() { int number; printf("\n Please Enter the Number You want to Convert : "); scanf("%d", &number); Decimal_to_Binary(number); return 0; }

**Output:**

In the above program, we have used a user-defined function Decimal_to_Binary.

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