Tips on Writing the Tax Program

TIP #1 

As indicated in the structure chart, it is a good design
decision to write three separate functions to compute the
tax:  one function for each tax schedule.  It will work well
to use a a switch statement to determine which function is
called to compute the tax.  (See TIP #4 for example code for
the switch statement.)

TIP #2

Code like this will get a "warning" from the compiler
because a real number is being assigned to an integer
variable:

int tax ;
if (txbleIncome > 34548) tax = 1521.08 +  0.093*(txbleIncome-34548) ;
		
Nevertheless the code above is OK.  It just computes the
real number corresponding to the expression, and then the
decimal part is "thrown away" when the value is assigned to
the variable.  The value that "tax" gets is incorrect by no
more than $0.99.

TIP #3

Code like this will do the job of computing the taxes:

if ( (txbleIncome >=  0) && (txbleIncome <=  5264) )
    tax =    0.00 + 0.01*(txbleIncome-0) ;
else if ( (txbleIncome >  5264) && (txbleIncome <=  12477) )
     tax =   52.64 + 0.02*(txbleIncome-5264) ;
else ... (... more of the same kind of code ...)

The kind of code above comes from direct copying of the
table.  However code like the code below works from the
bottom of a table towards the top:

       if (txbleIncome > 34548) tax = 1521.08 + 0.093*(txbleIncome-34548) ;
  else if (txbleIncome > 27337) tax =  944.20 + 0.08*(txbleIncome-27337) ;
  else if (txbleIncome > 19692) tax =  485.50 + 0.06*(txbleIncome-19692) ;
  else ...  (... more of the same kind of code ...)

This kind of code works too, and it requires fewer terms.
You can finish writing this code sooner and you are likely
to make fewer errors.

TIP #4

This example code shows how to treat the character input
of 'X', 'Y', or 'Z'

char  getStatus()
{ 
   char status ;

      // code here prints directions and prompt for the user.

   cin >> status ;

       // Note that you have to put char data in single quotes
       // so the compiler will not confuse char data with 
       // names for variables.

   if (status == 'X' || status == 'Y' || status == 'Z')
       return status ;   
   else 
   {
      cout << "BAD STATUS VALUE" << endl ;
      exit (-1) ;
   }
}

    // This function illustrates use of char data as the selector 
    // in a case statement.
int computeTax(char status, int txbleIncome)
{ 
  switch (status) 
  {
    case 'X': return (singleTax(txbleIncome)) ; break ;
    case 'Y': return (marriedTax(txbleIncome)) ; break ;
    case 'Z': return (headHouseTax(txbleIncome)) ; break ;
    default: cout << "BAD STATUS VALUE" << endl ;  return 0 ;
  }
}