Simple app to solve quadratic equation

quad-equatin.c

/*
 * quad-equatin.c
 *
 *  Copyleft (C) 2013  Sun Dro
 *
 * Simple app to solve quadratic equation
 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/* Simple math macros */
#define D(a,b,c) ((b<0)?((b*b)+(4*a*c)):(b*b)-(4*a*c))
#define X1(a,b,c) ((-b+sqrt(D(a,b,c)))/(2*a))
#define X2(a,b,c) ((-b-sqrt(D(a,b,c)))/(2*a))

int main(int argc, char *argv[])
{
    /* Check arguments */
    if (argc < 4)
    {
        printf("usage: %s [a] [b] [c]\n", argv[0]);
        printf("example: %s 1 4 4\n", argv[0]);
        return 0;
    }
 
    /* Get arguments */
    int a = atoi(argv[1]);
    int b = atoi(argv[2]);
    int c = atoi(argv[3]);
 
    /* Get the x-es */
    if (D(a,b,c) < 0) printf("There is no X\n");
    else printf("X1 = %3.1f, X2 = %3.1f\n", X1(a,b,c), X2(a,b,c));
 
    return 0;
}