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Trying to convert a fraction entered as a string into two seperate int variables

D22 (2)
I'm trying to create a program that accepts two numbers and turns them in fractions, multiply, divdes, adds, and subtracts them.

The user gets to input a fraction by putting it in as string and then the program separates the fraction and stores them into two int variables, numerator and denominator.

When I overloaded the >> operator I tried to separate the fraction inserted by the user using the stoi method but I keep getting the error "std::invalid_argument at memory location"

I realize that the problem might be that the stoi function is trying to convert '/' to a number. But I don't know how to fix it.

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<#include <iostream>
#include <string>
#include <sstream>

using namespace std;

class Rational
{
private:
		int numerator;
		int denominator;

public:
	Rational();
	Rational(int theNum, int theDen);
	Rational(int theNum);
	int getNumerator() const;
	int getDenominator() const;
	friend Rational operator+(const Rational &f1, const Rational &f2);
	friend Rational operator-(const Rational &f1, const Rational &f2);
	friend Rational operator*(const Rational &f1, const Rational &f2);
	friend Rational operator/(const Rational &f1, const Rational &f2);
	friend ostream& operator << (ostream& os, Rational& f1);
	friend istream& operator >> (istream& is, Rational& f1);
	friend bool operator== (const Rational &f1, const Rational &f2);
	friend bool operator>= (const Rational &f1, const Rational &f2);
	friend bool operator<= (const Rational &f1, const Rational &f2);
	friend bool operator> (const Rational &f1, const Rational &f2);
};

Rational::Rational() : numerator(0), denominator(1)
{}

Rational::Rational(int n, int d)
{
	numerator = n;
	denominator = d;
}

Rational::Rational(int n) 
{
	numerator = n;
	denominator = 1;
}

int Rational::getDenominator() const
{
	return denominator;
}

int Rational::getNumerator() const
{
	return numerator;
}


Rational operator+(const Rational &f1, const Rational &f2)
{
	int ansNum = (f1.numerator*f2.denominator) + (f2.numerator*f1.denominator);
	int ansDen = f1.denominator*f2.denominator;
	return Rational(ansNum, ansDen);
}

Rational operator-(const Rational &f1, const Rational &f2)
{
	int ansNum = (f1.numerator*f2.denominator) - (f2.numerator*f1.denominator);
	int ansDen = f1.denominator*f2.denominator;
	return Rational(ansNum, ansDen);
}

Rational operator*(const Rational &f1, const Rational &f2)
{
	int ansNum = f1.numerator*f2.numerator;
	int ansDen = f1.denominator*f2.denominator;
	return Rational(ansNum, ansDen);
}

Rational operator/(const Rational &f1, const Rational &f2)
{
	int ansNum = f1.numerator*f2.denominator;
	int ansDen = f1.denominator*f2.numerator;
	return Rational(ansNum, ansDen);
}

ostream& operator << (ostream& os, Rational& f1)
{
	os << f1.numerator << "/" << f1.denominator;
	return os;
}

istream& operator >> (istream& is, Rational& f1)
{
	string fraction;
	int i;
	getline(is, fraction);
	i = fraction.find('/');
	cout << "Is at position number:" << i << endl;
	string fract1 = fraction.substr(0,i);
	string fract2 = fraction.substr(i + 1);
	cout << fract1 << " " << fract2; 
	f1.numerator = stoi(fract1);
	f1.denominator = stoi(fract2);
	is >> f1.numerator;
	is >> f1.denominator;
	return is;
}

bool operator==(const Rational& f1, const Rational& f2)
{
	int leftSide = (f1.numerator*f2.denominator);
	int rightSide = (f1.denominator*f2.numerator);
	return (leftSide == rightSide);
}

bool operator>= (const Rational &f1, const Rational &f2)
{
	int leftSide = (f2.denominator*f1.numerator);
	int rightSide = (f1.denominator*f2.numerator);
	return (leftSide >= rightSide);
}

bool operator<= (const Rational &f1, const Rational &f2)
{
	int leftSide = (f2.denominator*f1.numerator);
	int rightSide = (f1.denominator*f2.numerator);
	return (leftSide <= rightSide);
}

bool operator> (const Rational &f1, const Rational &f2)
{
	int leftSide = (f2.denominator*f1.numerator);
	int rightSide = (f1.denominator*f2.numerator);
	return (leftSide > rightSide);
}

int main()
{
	Rational n1(1, 2), n2, n3;
	cout << n1 << endl;
	cin >> n2; // Input 2/3
	cout << n2 << endl;
	cout << n1 + n2 << endl;
	cout << n1 - n2 << endl;
	cout << n1 * n2 << endl;
	cout << n1 / n2 << endl;
	if (n1 == n2)
		cout << "n1 equals n2" << endl;
	else if (n1 > n2)
		cout << n1 << " greater than " << n2 << endl;
	else
		cout << n1 << " less than " << n2 << endl;
	cin >> n3; // Input -1/3
	cout << n3 << endl;
	if (n3 >= 0)
		cout << n3 << " is non-negative" << endl;
	else if (n3 <= 0)
		cout << n3 << " is non-positive" << endl;

	system("pause");
	return 0;

}
Last edited on
gunnerfunner (2127)
you can edit this function, if you wish, to overload the extraction operator:
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#include <iostream>
#include <sstream>
#include <string>

int main()
{
    std::cout << "Enter input \n";
    std::string input{}, numerator{}, denominator{};
    getline(std::cin, numerator, '/')&&getline(std::cin, denominator);
    int numTop{}, numDown{};
    std::istringstream streamTop(numerator);
    streamTop >> numTop;
    std::istringstream streamDown(denominator);
    streamDown >> numDown;
    //check numDown != 0;
    std::cout << numTop << "/" << numDown << '\n';
}

but there are still some other problems with your code - suggest you study the compiler error messages carefully

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