Why is my output wrong? - c++

Question

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
const double COUNTY_TAX = 0.02;
const double STATE_TAX = 0.04;
double totalSales;
void countyTax(double newCountyTax);
void stateTax(double newStateTax);
void total(double newTotal);
int main ()
{
cout << "Please enter the total dollar amount of sales: $";
cin >> totalSales;
countyTax(1);
stateTax(1);
total(1);
return 0;
}
void countyTax(double newCountyTax)
{
double newCountyTaxA;
newCountyTaxA = totalSales * COUNTY_TAX;
cout << "The county tax is: $" << newCountyTaxA << endl;
}
void stateTax(double newStateTax)
{
double newStateTaxA;
newStateTaxA = totalSales * STATE_TAX;
cout << "The State tax is: $" << newStateTaxA << endl;
}
void total(double newTotal)
{
double newTotalA, newStateTaxA, newCountyTaxA;
newTotalA = newStateTaxA + newCountyTaxA;
cout << "The total is: $" << newTotalA << endl;
}
hello guys! I am getting into modules in C++ and the above code compiles correctly but I can't seem to figure out why my output is wonky. I get the county tax and state tax to show properly but when the total shows I get "$nan" i was wondering if i could get some feedback on this? does it possibly have to do with the fact that within the module i am not using any global variables like i do with the totalSales and COUNTY_TAX and SALES_TAX and that when i declare newTotalA newStateTaxA newCountyTaxA they are declared but not assigned? just a tad confused here..THANKS!!!

Answer 1

the variables newStateTaxA and newCountyTaxA that are created and computed in countyTax and stateTax are local to those functions. Once the functions complete, those variables, and the values they contain, go away. In total you create new local variables with the same names. These have no relationship with the previously defined variables, apart from sharing names, and will not store the values previously computed in the other two functions.
The easiest solution, although not considered the most robust, is to create the two variables at the global scope, along with totalSales so that the values that they are assigned to in the two functions persist.
If you do not wish to use global variables (which I also don't care to use), you can declare them in your main function, and modify your other functions to return the calculated values:
double countyTax(double newCountyTax)
{
double newCountyTaxA;
newCountyTaxA = totalSales * COUNTY_TAX;
cout << "The county tax is: $" << newCountyTaxA << endl;
return newCountytaxA;
}
The calls in main() would then read:
newCountyTaxA = countyTax(1);

Answer 2

Your are doing a fundamental mistake here in the following code :
void total(double newTotal)
{
double newTotalA, newStateTaxA, newCountyTaxA;
newTotalA = newStateTaxA + newCountyTaxA;
cout << "The total is: $" << newTotalA << endl;
}
The Variables that you have created here "newStateTaxA", and "newCountyTaxA" does not have any relation to the other variables that you have created and assigned in the other methods, they are local for each method. You need to either make them global or return valued from those functions.

Answer 3

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
const double COUNTY_TAX = 0.02;
const double STATE_TAX = 0.04;
double totalSales;
void Taxes();
int main ()
{
cout << "Please enter the total dollar amount of sales: $";
cin >> totalSales;
Taxes();
return 0;
}
void Taxes()
{
double countyTax, stateTax, total;
countyTax = totalSales * COUNTY_TAX;
stateTax = totalSales * STATE_TAX;
total = countyTax + stateTax;
cout << "The County Tax is: $" << fixed << setprecision(2) << countyTax << endl;
cout << "The State Tax is: $" << fixed << setprecision(2) << stateTax << endl;
cout << "The total is: $" << fixed << setprecision(2) << total << endl;
}
here is what I came up with. Everything works and outputs as desired. I guess now I am wondering if this type of setup with one module and multiple calculations inside it considered good programming?