Binary to Decimal conversion

Problem Statement
Write a c program to convert binary number to decimal number
you should take the input by getchar() function
#include<stdio.h>
int twopow(int j);
int main()
{
  int i=0,b[50],j,sum;
  printf("enter the number in binary ");
  do
    {
      b[i]=getchar();
      i++;
    }
  while(b[i-1]!='\n');
  sum=0;
  for(j=0;j<i-1;j++)
    {
      printf("%d ",b[j]);
      sum=sum+(b[j]-48)*twopow(i-2-j);   // getchar stores the ansii code of numbers so b[j]-48
    }
  printf("the equivalent decimal number is %d \n",sum);
  return 0;
}
int twopow(int j)
{
  int mul,i;
  mul=1;
  for(i=0;i<j;i++)
    {
      mul=mul*2;
    }
  return mul;
}