``````// rational.cpp - Script 9.5

#include <iostream>

#include <string>

// Declare the class.
class Rational {

public:

// Constructor:
Rational(int num, int denom);

// The overloaded methods that implement
// arithmetic functions:
Rational operator+(Rational rhs);
Rational operator-(Rational rhs);
Rational operator*(Rational rhs);
Rational operator/(Rational rhs);

void print();

private:
// normalize() will take care of transforming
// numerator and denominator into a well defined
// format.
void normalize();

int numerator;
int denominator;
};

// Define the constructor.
Rational::Rational(int num, int denom) {

// Assign the values.
numerator = num;
denominator = denom;

// Call normalize in case the user
// passed "garbage" to the object.
normalize();
}

Rational Rational::operator+(Rational rhs) {

// a c a*d c*b a*d + c*b
// - + - = --- + --- = ---------
// b d b*d b*d  b*d

int a = numerator;
int b = denominator;
int c = rhs.numerator;
int d = rhs.denominator

// Calculate the new numerator and denominator.
int e = a*d + c*b;
int f = b*d;

// Return the resulting Rational
return Rational(e,f);
}

Rational Rational::operator-(Rational rhs) {

// a c a -c
// - - - = - + --
// b d b d

// Change the sign of the right-hand side
rhs.numerator = -rhs.numerator;

// Now just add the two, using the operator+ method call.
return operator+(rhs);
}

Rational Rational::operator*(Rational rhs) {

// a c a*c
// - * = ---
// b d b*d

int a = numerator;
int b = denominator;
int c = rhs.numerator;
int d = rhs.denominator;

// Calculate the new numerator and denominator.
int e = a*c;
int f = b*d;

// Return the resulting Rational.
return Rational(e,f);
}

Rational Rational::operator/(Rational rhs) {

// a c a d
// - / - = - * -
// b d b c

// Invert the right-hand side
int t = rhs.numerator;
rhs.numerator = rhs.denominator;
rhs.denominator = t;

// Now just multiply the Rationals.
return operator*(rhs);
}

// Define the methods.
void Rational::print() {
std::cout << numerator << "/" << denominator;
}

void Rational::normalize() {

//Check the signs.
if (denominator < 0) {
// "Move" the sign to the nominator.
numerator = -numerator;
denominator = -denominator;
}

// Calculate the greatest common denominator of a/b
// using Euclid's algorithm.
int a = abs(numerator);
int b = abs(denominator);
while (b > 0) {
int t = a % b;
a = b;
b = t;
}

// Divide both numbers by a.
numerator /= a;
denominator /= b;
}

int main() {

// Create two Rationals: 2/16 and 7/8.
Rational f1(2,16);
Rational f2(7,8);

Rational res = f1 + f2;
f1.print();
std::cout << " + ";
f2.print();
std::cout << " == "
res.print();
std::cout << "\n";

// Test subtraction.
res = f1 - f2;
f1.print();
std::cout << " - ";
f2.print();
std::cout << " == ";
res.print();
std::cout << "\n";

// Test multiplication.
res = f1 * f2;
f1.print();
std::cout << " * ";
f2.print();
std::cout << " == ";
res.print();
std::cout << "\n";

// Test division.
res = f1 / f2;
f1.print();
std::cout << " \ ";
f2.print();
std::cout << " == ";
res.print();
std::cout << "\n";

std::cin.get();
return 0;
}``````

Why isn't this program compileing? When I compile it it comes up with this error:
Line file message
59 C:\Dev-Cpp\rational.cpp expected `,' or `;' before "int"

The code is from a book I'm using so it should compile but isn't. Can anybody help?

I also need help understanding the code if anyone can help with that or point me in the right direction? Because it's gobbledygook to me. Iv'e been using this book and have been able to understand everything up till now but with the above code I'm totally lost.

For example what does the parameter (Rational rhs) in line 47 mean? Is it the same as one of the parameters in the constructor i.e int num and int denom on line 35?

Line 56.

``int d = rhs.denominator``

This misses an ending semicolon.

Line 47:
When adding two variables of the type Rational like:

``f1 + f2;``

What happens function-call wise is:

``f1.operator+(f2);``

so Rational rhs is the Rational that is added to the Rational with which we start.

Thanks. I understand what you are saying which helps a little but I'm still having trouble understanding the code as a whole. I need someone to break it down into layman's terms so I can understand it.

Rational Rational::operator+(Rational rhs) {
int a = numerator;
int b = denominator;
int c = rhs.numerator;
int d = rhs.denominator
int e = a*d + c*b;
int f = b*d;
return Rational(e,f); }

Analysis from book:
This is just basic math. The function calculates the numerator and the denominator of the result, and then it returns a new Rational based on these values. As you can see in the script, a comment describes how fractions are added (where?) Temporary variables are used to keep the code clean and readable.(I presume the temporary variables are int e and f?)

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