program for Converting Yen, Euro And Pounds To Dollars

[DragonOsman]

For my book, I'm writing a program that would convert Yen, Euros and Pounds to Dollars. I checked on Google and found that there's 0.0098 Yen in one Dollar, 1.13 Euro to one Dollar and 1 Pound to 1.32 Dollars. I'm not sure how to use those to convert from those currencies to Dollars, though, so that's what I need help on.

I'm assuming that to convert from Yen to Dollars, I should multiply the amount in Yen by the conversation rate. Is that correct? For the other two, would multiplying do it? Or is there something else I have to do? From what I saw on Google, it seems like converting from Euros to Dollars via multiplication gives me an answer that's off by one or two coins.

[Duthomhas]

A conversion rate is always A → B, which is B = A*rate.
To go backwards you'll need to divide: A = B/rate;

Hope this helps.

[DragonOsman]

Since Euro and Pounds are both greater than Dollars, would it be good to divide to convert to Dollars? Or should I multiply here as well?

And if it's multiplication in either case, then it's like this, right?

Dollars = Yen * 0.0098
Dollars = Euro * 1.13
Dollars = Pound * 1.32

Or would it be better to divide for the Yen to Dollar conversion since the Yen is smaller?

[Duthomhas]

It doesn't make any difference whether larger or smaller. What matters is that the rate is a scalar that satisfies the condition I gave you above.

1 yen == 0.0098 dollar
Conversion rate is yen→dollar == 0.0098

If I have 300 yen, yen*rate = dollars, and 300yen*0.0098 = 2.94dollars.
If I have 3 dollars, dollars/rate = yen, and 3.00dollars/0.0098 = about 306 yen.

[DragonOsman]

Yeah, I'm aware that they're constantly changing and aren't static.

@Duoas: Right, I get it. I'll just multiply them all, then.

[Duthomhas]

I'm guessing I misunderstood your question. You weren't asking about the math, were you?

Floating-point arithmetic should be exact enough to get you the correct number of pennies/whatever the base unit is. Is there a specific Euro→Dollar test case that you can share?

[DragonOsman]

This is the code I have right now.

// Osman Zakir
// 9 / 15 / 2016
// Stroustrup's Programming: Principles and Practice Using C++ 2nd Edition Chapter 4 Section 4
// "Try This" exercise
// Program to convert Yen, Euros and Pounds into Dollars
// Yen to Dollars = amount of Yen to convert * number of Yen in Dollars
// Euro to Dollars = amount of Euro to convert * rate of Euro to Dollars
// Pound to Dollars = amount of Pounds to convert * rate of Pounds to Dollars

#include "std_lib_facilities.h"

double get_money_amount();
char get_currency();
double calculate_converted_amount(char currency, const double yen_in_dollars, const double euro_to_dollars, const double pound_to_dollars, double amt_of_money);
void print_converted_amount(const double converted_amount, const char currency);

int main()
{
	constexpr double yen_in_dollars = 0.0098;
	constexpr double euro_to_dollars = 1.12;
	constexpr double pound_to_dollars = 1.32;

	double amt_of_money = get_money_amount();
	char currency = get_currency();
	double converted_amount = calculate_converted_amount(currency, yen_in_dollars, euro_to_dollars, pound_to_dollars, amt_of_money);
	print_converted_amount(converted_amount, currency);
	
	keep_window_open();
	cin.ignore();
	return 0;
}

double get_money_amount()
{
	cout << "Please enter amount of money:\n";
	double amt_of_money = 0;
	cin >> amt_of_money;
	cin.ignore(32767, '\n');
	return amt_of_money;
}

char get_currency()
{
	cout << "Please enter currency (e for Euro, y for Yen, p for Pounds):\n";
	char currency = 0;
	cin >> currency;
	cin.ignore(32767, '\n');
	return currency;
}

double calculate_converted_amount(char currency, const double yen_in_dollars, const double euro_to_dollars, const double pound_to_dollars, double amt_of_money)
{
	double converted_amount;
	if (currency == 'e')
	{
		converted_amount = amt_of_money * euro_to_dollars;
	}
	else if (currency == 'y')
	{
		converted_amount = amt_of_money * yen_in_dollars;
	}
	else if (currency == 'p')
	{
		converted_amount = amt_of_money * pound_to_dollars;
	}
	else
	{
		simple_error("Sorry, I don't know that currency");
	}
	return converted_amount;
}

void print_converted_amount(const double converted_amount, const char currency)
{
	cout << "Your money in ";

	if (currency == 'e')
	{
		cout << "Euros";
	}
	else if (currency == 'p')
	{
		cout << "Pounds";
	}
	else if (currency == 'y')
	{
		cout << "Yen";
	}

	cout << " is " << converted_amount << " Dollars.\n";
}

Test cases: 45 Yen to Dollars is $0.441. 45 Euros to Dollars is $50.4. And 45 Pounds to Dollars is $59.4.

Conversion rates used are:
Pounds to Dollars: 1.32
Yen to Dollars: 0.0098
Euro to Dollars: 1.12

You can tell that by looking at the code above, though, of course.

[Duthomhas]

That looks right. Not all conversions will come out to even amounts of money, so 44.1 cents is okay. If you like you can round those down, but I wouldn't bother.

Your code is otherwise pretty nicely structured. There are a few beginner issues I would not do, but there is really nothing wrong with it.

One suggestion: use a table. C++ provides a std::map for that purpose, but anything that associates the two values works (a pair of arrays, an array of pairs or structs, etc).

string currency_rate_names      [] = { "dollars", "euros", "pounds", "yen" };
double currency_rates_to_dollars[] = { 1.0,       1.12,    1.32,     0.0098 };

struct conversion_rate
{
  string name;
  double rate_to_dollar;
};
conversion_rate conversion_rates_to_dollars[] = 
{
  { "dollars", 1.0    },
  { "euros",   1.12   },
  { "pounds",  1.32   },
  { "yen",     0.0098 }
};

Here's my version:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

#include <cctype> #include <ciso646> #include <iostream> #include <map> #include <string> std::map <std::string, double> to_dollar_rates { { "Dollars", 1.0000 }, { "Euros", 1.1200 }, { "Pesos", 0.0520 }, { "Pounds", 1.3200 }, { "Yen", 0.0098 } }; std::string totitle( const std::string& s ) { std::string r( s ); for (char& c : r) c = tolower( c ); for (char& c : r) { c = toupper( c ); break; } return r; } std::string select_currency( const std::string& prompt ) { std::string currency_name; std::cout << prompt << "\n"; for (auto rate_info : to_dollar_rates) std::cout << " " << rate_info.first << "\n"; std::cout << ": "; std::getline( std::cin, currency_name ); currency_name = totitle( currency_name ); if (!to_dollar_rates.count( currency_name )) throw "Not a valid currency"; std::cout << "\n"; return currency_name; } int main() { try { std::string from_currency = select_currency( "Select a FROM currency:" ); std::string to_currency = select_currency( "Select a TO currency:" ); double from_amount; std::cout << "Enter an amount to convert: "; std::cin >> from_amount; double dollars = from_amount * to_dollar_rates[ from_currency ]; double to_amount = dollars / to_dollar_rates[ to_currency ]; std::cout << from_amount << " " << from_currency << " is " << to_amount << " " << to_currency << ".\n"; } catch (const char* s) { std::cout << s << "\n"; return 1; } }

Select a FROM currency: Dollars Euros Pesos Pounds Yen : yen Select a TO currency: Dollars Euros Pesos Pounds Yen : dollars Enter an amount to convert: 5000 5000 Yen is 49 Dollars.

Hope this helps.

[DragonOsman]

I haven't learned about maps yet in the book. It mentioned it, but it'll teach about them in a later chapter. But yeah, thanks.

[SakurasouBusters]

@Duoas
How to make your code and your output look like that? I am curious.

[shadder]

use --- at the end of your code and paste the output
http://www.cplusplus.com/articles/z13hAqkS/