# C Program to Convert Binary Number to Decimal and vice-versa

In this example, you will learn to convert binary number to decimal and decimal number to binary manually by creating a user-defined function.

To understand this example, you should have the knowledge of following C programming topics:

Visit this page to learn how to convert binary number to decimal.

## Example 1: Program to convert binary number to decimal

``````#include <stdio.h>
#include <math.h>
int convertBinaryToDecimal(long long n);

int main()
{
long long n;
printf("Enter a binary number: ");
scanf("%lld", &n);
printf("%lld in binary = %d in decimal", n, convertBinaryToDecimal(n));
return 0;
}

int convertBinaryToDecimal(long long n)
{
int decimalNumber = 0, i = 0, remainder;
while (n!=0)
{
remainder = n%10;
n /= 10;
decimalNumber += remainder*pow(2,i);
++i;
}
return decimalNumber;
}
``````

Output

```Enter a binary number: 110110111
110110111 in binary = 439
```

Visit this page to learn, how to convert decimal number to binary.

## Example 2: Program to convert decimal number to binary

``````#include <stdio.h>
#include <math.h>
long long convertDecimalToBinary(int n);

int main()
{
int n;
printf("Enter a decimal number: ");
scanf("%d", &n);
printf("%d in decimal = %lld in binary", n, convertDecimalToBinary(n));
return 0;
}

long long convertDecimalToBinary(int n)
{
long long binaryNumber = 0;
int remainder, i = 1, step = 1;

while (n!=0)
{
remainder = n%2;
printf("Step %d: %d/2, Remainder = %d, Quotient = %d\n", step++, n, remainder, n/2);
n /= 2;
binaryNumber += remainder*i;
i *= 10;
}
return binaryNumber;
}
``````

Output

```Enter a decimal number: 19
Step 1: 19/2, Remainder = 1, Quotient = 9
Step 2: 9/2, Remainder = 1, Quotient = 4
Step 3: 4/2, Remainder = 0, Quotient = 2
Step 4: 2/2, Remainder = 0, Quotient = 1
Step 5: 1/2, Remainder = 1, Quotient = 0
19 in decimal = 10011 in binary```