indirection requires pointer operand and expected expression errors - compilation

Question

I keep getting errors similar to these:
pitstop.cpp:36:23: error: indirection requires pointer operand
('double' invalid)
cost = UNLEADED * gallons;
^ ~~~~~~~
pitstop.cpp:40:14: error: expected expression
cost = SUPER * gallons; ^
#include <iostream>
#include <iomanip>
using namespace std;
#define UNLEADED 3.45;
#define SUPER {UNLEADED + 0.10};
#define PREMIUM {SUPER + 0.10};
/*
Author: Zach Stow
Date:
Homework
Objective:
*/
double cost, gallons;
string gasType, finish, stop;
int main()
{
for(;;)
{
cout <<"Hi, welcome to Pitstop.\n";
cout <<"Enter the type of gas you need:";
cin >> gasType;
cout << endl;
cout <<"Enter the amount of gallons you need:";
cin >> gallons;
cout << endl;
if(gasType == "finish" || gasType == "stop")break;
else if(gasType == "UNLEADED")
{
cost = UNLEADED * gallons;
}
else if(gasType == "SUPER")
{
cost = SUPER * gallons;
}
else if(gasType == "PREMIUM")
{
cost = PREMIUM * gallons;
}
}
cout <<"You need to pay:$" << cost << endl;
return(0);
}

Answer 1

Not a c++ expert, but I'm sure that to define a constant you just need to use the #define directive followed by the symbol and by the value you want to assign to it (even if the value itself is an expression, even if such expression is referencing another constant), the braces and the trailing semicolon are excessive:
// [...]
#define UNLEADED 3.45
#define SUPER (UNLEADED + 0.10)
#define PREMIUM (SUPER + 0.10)
//[...]
It compiled at the first attempt with such corrections.

Answer 2

The cause of the error is the semi colon at the end of the #define directive.
You have also used the incorrect type of brackets, try this instead:
#define UNLEADED 3.45
#define SUPER (UNLEADED + 0.10)
#define PREMIUM (SUPER + 0.10)
Note that when you use the #define directive whatever follows #define is substituted into your code. In this case after the preprocessor ran your code looked like this:
else if(gasType == "UNLEADED")
{
cost = UNLEADED 3.45; * gallons;
}
else if(gasType == "SUPER")
{
cost = {UNLEADED + 0.10}; * gallons;
}
else if(gasType == "PREMIUM")
{
cost = PREMIUM {SUPER + 0.10}; * gallons;
}
The reason you were getting the indirection requires pointer operand error was the compiler trying to interpret this statement:
* gallons;
Because the * operator only has a single argument it is interpreted as a pointer dereference, luckily for you the gallons variable is not a pointer type. If gallons had been declared as a pointer type i.e. double cost, *gallons; and the cin wasn't there the code would compile but not do what you expect, probably throwing a segfault.
Macros defined with #define can be very powerful and very dangerous. There is usually a better way to achieve things in c++. In this case UNLEADED, SUPER_UNLEADED and PREMIUM could be declared as const double type i.e.
const double unleaded = 3.45;
const double super = unleaded + 0.10;
const double premium = super + 0.10;