Convert Binary Number to Decimal Number in C | C Program

Here's a C program to convert a binary number to a decimal number with output and proper explanation. This program makes use of C concepts like While loop, IF-Else and Modulus. The program also uses C's math.h header file and power function pow(i, j).

# include <stdio.h>
# include <conio.h>
# include <math.h> 
void main() 
{ 
 int i = 0, j = 0, sum = 0 ; 
 long int n ; 
 clrscr() ; 
 printf("Enter the binary number : ") ; 
 scanf("%ld", &n) ; 
 if(n > 0) 
 { 
  i = n % 10 ; 
  if(i == 0 || i == 1) 
  { 
   while(n != 0) 
   { 
    i = n % 10 ; 
    sum = sum + i * pow(2, j) ; 
    n = n / 10 ; 
    j ++ ; 
   } 
  } 
 } 
 if(sum == 0 && n < 0) 
  printf("\nThe number is not a binary number") ; 
 else 
  printf("\nThe equivalent decimal number is : %d", sum) ; 
 getch() ; 
} 

Output of above program is 

Enter the binary number : 1100
The equivalent decimal number is : 12

Enter the binary number : 12
The number is not a binary number

How to convert binary number to decimal? Here's a basic method to convert a binary number to decimal form. Suppose there are n digits in your binary number. So the formula to get decimal equivalent of this binary number is - (Here nth digit is the leftmost digit and 1st digit is the rightmost digit.)

Decimal number = (value of nth digit) * 2 ^(n-1) + (value of n-1 th digit) * 2 ^(n-2) + (value of n-2 th digit) * 2 ^(n-3) +........ + (value of 1st digit) * 2 ⁽⁰⁾

e.g. b = 10010. The decimal value is - 

Decimal number = 1 * 2 ⁴ + 0 * 2 ³ + 0 * 2 ² + 1 * 2 ¹ + 0 * 2 ⁰ = 16 + 2 = 18.

Explanation of above program

Our program also uses the same process described above. We are using Math.H header file for the mathematics function pow(i, j) to calculate power.