C program to calculate income tax using default arguments

#include<stdio.h>
#include<stdarg.h>
struct income_tax { int itax, int icm;};
#define income_tax(...) income_tax((struct income_tax){.itax=0,.icm,  __VA_ARGS__})
int main(int itax, int icm)
{
 printf ("Enter your income: ");
    scanf ("%d", &icm);
if (icm >= 250000 && icm <= 500000)
    {
        itax = itax + 0.09 * (icm - 250000);
    }
if (icm >= 500000 && icm <= 1000000)
    {
        itax = itax + 0.20 * (icm - 500000);
    }
if (icm >= 1000000)
    {
        itax = itax + 0.30 * (icm - 1000000);
    }
 printf ("Your net income tax is: %d", itax);
return 0;
}

Output:

Enter your income: 4000000
Your net income tax is: 13500