#include <stdio.h>
#include <string.h>

int formateo_miles(int n, char str[20])
{
	char fraccion[5];

	if (n / 1000 > 0)
	{
		formateo_miles(n / 1000, str);
		sprintf(fraccion, ",%.3d", n % 1000);
	}
	else
	{
		sprintf(fraccion, "%d", n % 1000);
	}
	strcat(str, fraccion);
	return n;
}

int main()
{
	char str[20];
	double n = 12345678.455;
	int pent = int(n);
	double pdec = (n - pent) * 100;

	memset(str, 0, 20);
	formateo_miles(pent, str);
	printf("%s.%2.0lf", str, pdec);
	return 0;
}