super simple currency converter switch acting oddly? - c++

Question

This was an exercise from Principles and Practice Using C++ to make a basic currency converter using if checks then to remake it with switches. Everything runs pretty good except or my middle switch. It doesn't seem to work like the rest of the program. Every other one is fine with me entering in data like 111y, 111p but when working with euros it NEEDS a whitespace or else it will go to the default switch. I did a break point and currency is not being set to e or E and it's only with the euros!
I hope it isn't anything too silly, but it's got me confused Bjarne doesn't explain this one :P I don't have #include iostream in the code because it's all handled with *std_lib_facilities* Just wanted to say that before someone points it out XD
#include "std_lib_facilities.h"
using namespace std;
int main()
{
double dollar = 0;
char currency = ' ';
const double yen = 0.010;
const double euro = 1.31;
const double pound = 0.65;
double sum = 0;
cout << "Please enter amount and Y for yen or E for Euro or P for pound.\n";
cin >> dollar >> currency;
switch(currency)
{
case 'Y': case'y':
{
sum = dollar * yen;
cout << dollar << " is equal to " << sum << " yen.\n";
break;
}
case 'E': case'e':
{
sum = dollar * euro;
cout << dollar << " is equal to " << sum << " euro.\n";
break;
}
case 'P': case'p':
{
sum = dollar * yen;
cout << dollar << " is equal to " << sum << " pound.\n";
break;
}
default:
cout << "Wrong values...\n";
break;
}
keep_window_open();
return 0;
}

Answer 1

Since dollar is a double, the E or e gets interpreted as part of the exponent of the number (as in 2e-2) when you extract it. Since there are no digits after it, the extraction does not complete and cin goes into the fail state. The read of currency is then skipped, never changing it from the initial value of ' '. When you enter a space, the extraction of dollar ends at the space and currency is read as expected.
To fix it, you could try several things. You could require a space between the amount and the currency indicator. You could read it in as a string and attempt to parse it yourself. You could pick a different symbol for euros.
In any case, you should check the state of the cin after you're done reading from it.