C program to calculate income tax using default arguments

#include<stdio.h>
#include<conio.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;
}