#include <stdio.h>


int main()
{
	int bin=123, bcd;

	int n, dig, num, count;

	num = bin;
	count = 0;
	bcd = 0;
	for (n=0; n<4; n++) {
		dig = num%10;
		num = num/10;
		bcd = (dig<<count)|bcd;
		count += 4;
	}
	printf("binary: %d  bcd: %x\n",bin,bcd);
	return 0;
}

Results

binary: 123  bcd: 123