IIR low pass cutoff calculator

iirc.c

/*
 Calculate filter constant for a single pole low pass IIR filter
 given cut off freq and the sample rate.
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(int argc,char *argv[])
{
	if(argc<2)
	{
		printf("usage:f1,f2\n");
		return -1;
	}
	
	double cutoff = strtof(argv[1],NULL);
	double rate = strtof(argv[2],NULL);
	
	double omega_c = 2*M_PI*(cutoff/rate);
	double b = 2 - cos(omega_c) - sqrt(pow(2-cos(omega_c),2)-1);
	
	printf("b = %.15g\n",b);
	return 0;
}