Programming issues. Writing a tax calculator: part 2.

After playing around with the tax calculator I managed to write the zero or negative number control inside the method as I wanted before. It may seem too easy for expert programmers but for me was a bit tricky. First I used the while loop keyword and saw the printf line printing itself on the screen inside an infinite loop! Then I woke up and used the if/else statements.
The next problem was stopping the program from printing the lines that were at the main() function. The print method call, was printing 0’s anyway. So another if/else control on the print method was enough. I did change the print method, at the header file, in order to make it accept a single argument. I’m not sure if it was necessary for print to work as I wanted. Stop! Let’s test it! No! Here is the error: ‘p’ undeclared (first use in this function) which is quite normal, because the method doesn’t expect any variable or argument. However, I could try to declare the variable inside the method, but when I did that and try to compile the program, xcode crashed! Yeah! Am I good or what? Anyway, declaring inside a method a value that should be retrieved from outside doesn’t make much sense anyway.
So here is the code:
The .h file

#import
#import

@interface TAX: Object
{
double price;
}

-(void) setPrice: (int) p;
-(void) print: (int) p;

@end

and the .m file:

#import
#import
#import “ivacalc.h”

@implementation TAX;

-(void) print: (int) p
{
price = p;

if ( p > 0 )
{
printf(”The price is %.2f and the tax is %.2f.\nThe sum is %.2f\n”, price, price * 0.19, price + (price*0.19));
}
else
{
printf(”exiting\n”);
}
}

-(void) setPrice: (int) p
{
if (p < 1) // don’t do calculation for negative numbers
{
printf(”The price is 0 or negative!\n”);
p = 0;
}
else
p = price;
}

@end

int main(int argc, char *argv[])
{
int j;

TAX *myTax = [[TAX alloc] init]; // allocating and initializing a TAX-fellow class!

printf(”Price: “);
scanf(”%i”, &j);
printf(”\n”);

[myTax setPrice: j];
[myTax print: j];

[myTax free];

return 0;
}

Now the program does check if the number entered is 0 or negative and prints an error message if it is.