'SalesTaxPct' was not declared in this scope - c++

Question

I am new to C++. I am struggling with the pass by value thing, and no one can explain what I am doing wrong to me in a way I can understand. I know this is my fault, but Ii am asking for help with my code. HELP PLEASE!
#include <iostream>
using namespace std;
double getValues();
double getSalesTax(double SalesTaxPct);
double gettotal_price(double base, double opt);
void PrintFinal(double base,double opt,double SalesTaxPct);
// function to control all other functions
int main()
{
getValues();
getSalesTax(SalesTaxPct);
PrintFinal(base,pt,SalesTaxPct);
}
// function to calculate sales tax percent into decimal
double getSalesTax( double SalesTaxPct )
{
double SalesTax;
SalesTax = SalesTaxPct / 100;
return SalesTax;
}
// function to find total
double gettotal_price(double base, double opt, double SalesTax)
{
return = (base + opt) * (1 + SalesTax);
}
// function to show user all values input and also total
void PrintFinal(double base, double opt, double SalesTaxPct)
{
cout << "Base vehicle price: $" << base << endl;
cout << "Options Price: $" << opt << endl;
cout << "Sales tax pct: " << SalesTaxPct << "%" << endl;
cout << "Total vehicle price: $" << gettotal_price(double base, double opt, double SalesTax) << endl;
}
// function to get input values
void getValues()
{
double base, double opt, double SalesTaxPct;
cout << "Enter a base vehicle price: " << endl;
cin >> base;
cout << "Enter options price: " << endl;
cin >> opt;
cout << "Enter a sales tax percent: " << endl;
cin >> SalesTaxPct;
}

Answer 1

When you are in main, let's go over what the program sees:
int main()
{
getValues();
getSalesTax(SalesTaxPct);
PrintFinal(base,pt,SalesTaxPct);
}
The only variables that your program knows about at this point are: getValues(), getSalesTax(), gettotal_price(), and PrintFinal(). The warning is telling you that at this point of your program, SalesTaxPct was not declared yet, and looking at our list of variables / functions that the program knows about, we see that, indeed, SalesTaxPct is not on the list. Where do we expect the value of SalesTaxPct to come from?
It looks like that comes from the function getValues, and we are getting it from user input. However, any time that you have { ... }, the stuff inside the braces cannot be accessed outside. Therefore, SalesTaxPct is only "in scope" inside the function getValues. If you want it to be accessible outside of that function (which you do), you need to change things around a bit.
int main()
{
double base;
double opt;
double SalesTaxPct;
getValues(base, opt, SalesTaxPct);
getSalesTax(SalesTaxPct);
PrintFinal(base, opt, SalesTaxPct);
}
Now all of our variables still exist when we need them in main. However, there is still a problem here. We want the changes we pass into getValues to change the variables in main. This means we cannot pass "by value" because that will first make a copy, and then change those copies (not what we want). Instead, we need to say that the changes we make need to be returned from the function some how:
void getValues(double & base, double & opt, double & SalesTaxPct);
That little & there means that rather than making a copy and changing that copy, we are telling the function to operate on the variable we pass in directly. This is referred to as "pass by reference".
There are some similar problems in other parts of your code, but perhaps now you can figure out how to fix them.