#include <stdio.h>
flaot tax;
int price;
float total;
int main()
{
tax=0.15;
printf("What is the Cost?");
scanf("%d", &price);
total=(price*tax)+price;
printf("\nTotal cost = %2.2lf\n",total);
return 0;
}
I think that does the same thing as what u were trying to do but without the define bit, calling total a flaot instead
is this any help?
(i found it useful for me even if it didnt help you)

nez