divide the given no by two n store the remainder in stack 
and divide again by 2 to quotent the process gong on....
n store all the remainder in the same stack....
n in last pop all the element from stack n print it.

let the number be n
int bin(int n)
{
static int sum=0;

if(n>1)
{
rem=n%2;
sum = sum *10 +rem;
n=n/2;
bin(n);
}
else
{
sum=sum*10+1;
}
return sum;
}

It's very simple.
Firstly, the binary no. of 0 is 0000.
After that if you want to know the binary no. of 1 then 
jaust add 1 to binary no. of 0 i.e. 0000.So, now the ans 
will be 0001.But,remember here 1+1=10.So, now if you want 
binary no. of 2 then add 1 to binary no. of 1 i.e. 0001.So, 
the binary no. of 2 will be 0010.
I hope you got your question answer.

#include<stdio.h>
#include<conio.h>

int main()
{
	int i,number;
	printf("Enter the Number\n");
	scanf("%d",&number);

	for(i=7;i>=0;i--)
	{
		if((1<<i) & number)
			 printf("1");
		else
			 printf("0");
	}
}

divide no. by 2 till 1 is not coming in quotient, then it 
write from bottom to top