C program to covert 'Decimal to Binary' and 'Binary to Decimal'

Binary Decimal Conversion

/* C programming source code to convert either binary to decimal or decimal to binary according to data entered by user. */
/* From http://www.programiz.com/ */

#include <stdio.h>
#include <math.h>
int binary_decimal(int n);
int decimal_binary(int n);
int main()
{
   int n;
   char c;
   printf("Instructions:\n");
   printf("1. Enter alphabet 'd' to convert binary to decimal.\n");
   printf("2. Enter alphabet 'b' to convert decimal to binary.\n");
   scanf("%c",&c);
   if (c =='d' || c == 'D')
   {
       printf("Enter a binary number: ");
       scanf("%d", &n);
       printf("%d in binary = %d in decimal", n, binary_decimal(n));
   }
   if (c =='b' || c == 'B')
   {
       printf("Enter a decimal number: ");
       scanf("%d", &n);
       printf("%d in decimal = %d in binary", n, decimal_binary(n));
   }
   return 0;
}

int decimal_binary(int n)  /* Function to convert decimal to binary.*/
{
    int rem, i=1, binary=0;
    while (n!=0)
    {
        rem=n%2;
        n/=2;
        binary+=rem*i;
        i*=10;
    }
    return binary;
}

int binary_decimal(int n) /* Function to convert binary to decimal.*/

{
    int decimal=0, i=0, rem;
    while (n!=0)
    {
        rem = n%10;
        n/=10;
        decimal += rem*pow(2,i);
        ++i;
    }
    return decimal;
}

#include<stdio.h>
#include<stdlib.h>
int main()
{
int decNumber,*arr,counter=0,loop=0,rem=0,copy1,copy2;
printf("\nEnter a Decimal Number:");
scanf("%d",&decNumber);
copy1=decNumber;
copy2=decNumber;
while(copy1 != 0)
{
counter++;
copy1/=2;
}
arr=(int *)calloc(counter,sizeof(int));
for(loop=0;loop<counter;loop++)
{
rem=copy2%2;
arr[loop]=rem;
copy2/=2;
}
printf("\nThe Binary representation of %d is: ",decNumber);
for(loop=counter-1;loop>=0;loop--)
{
printf("%d",arr[loop]);
}

return 0;

}