C ++ Fraction class operator overload exercise

# Include <iostream> using namespace std; int GreatestCommonDivisor (int m, int n) // calculate the maximum approximate number of moving phase division {int r; do {r = m % n; m = n; n = r;} while (r! = 0); return m;} class Fraction; // ostream & operator <(ostream & out, const Fraction & fra ); // istream & operator> (istream & in, const Fraction & fra); // The three actions meet the compilation logic of vc6.0 and declare class Fraction {private: int fenzi, fenmu; // numerator, denominator public: Fraction (){}~ Fraction () {} Fraction (int fenzi, int fenmu); Fraction operator + (const Fraction & fra) const; Fraction operator-(const Fraction & fra) const; fraction operator * (const Fraction & fra) const; Fraction operator/(const Fraction & fra) const; friend ostream & operator <(ostream & out, const Fraction & fra ); // I/o overload must use the friend element overload friend istream & operator> (istream & in, const Fraction & fra); void setValue (int mu, int zi) ;}; Frac Tion: Fraction (int zi, int mu): fenzi (zi), fenmu (mu) {if (mu = 0) {cout <"the denominator cannot be 0! "<Endl; exit (0) ;}} ostream & operator <(ostream & out, const Fraction & fra) {if (fra. fenmu <0) out <"(-" <fra. fenzi <"/" <-fra. fenmu <")"; // The negative score shows else if (fra. fenzi <0) out <"(-" <-fra. fenzi <"/" <fra. fenmu <")"; else if (fra. fenmu = 1) out <fra. fenzi; // else out <fra. fenzi <"/" <fra. fenmu; // return out;} istream & operator> (istream & in, Fraction & fra) {int mu, zi; cout <"Enter denominator and Numerator" <endl; in> mu>> Zi; fra. setValue (mu, zi); return in;} void Fraction: setValue (int mu, int zi) {fenmu = mu; fenzi = zi;} Fraction :: operator + (const Fraction & fra) const {int a = fenzi, B = fenmu; // ▲▲▲ important ▲▲/// be sure to use const, if this parameter is not used, the data of the previous operation will be assigned to the next operation of l-value. // because the const function cannot change the internal variables of the class, you must use a replacement, if you use the friend overload here, // can effectively avoid this problem, because the friend overload operator has two referenced parameters a = fra. fenmu * fenzi + fra. fenzi * fenmu; B * = fra. fenmu; int g = GreatestCommonDivisor (a, B); if (g! = 1) {a/= g; B/= g;} return Fraction (a, B);} Fraction: operator-(const Fraction & fra) const {int a = fenzi, B = fenmu; a = fra. fenmu * fenzi-fra.fenzi * fenmu; B * = fra. fenmu; int g = GreatestCommonDivisor (a, B); if (g! = 1) {a/= g; B/= g;} return Fraction (a, B);} Fraction: operator * (const Fraction & fra) const {int a = fenzi, B = fenmu; a * = fra. fenzi; B * = fra. fenmu; int g = GreatestCommonDivisor (a, B); if (g! = 1) {a/= g; B/= g;} return Fraction (a, B);} Fraction: operator/(const Fraction & fra) const {return * this * Fraction (fra. fenmu, fra. fenzi);} void main () {Fraction a (1, 2); Fraction B (1, 4); Fraction c = a + B; Fraction d = a-B; fraction e = B-a; Fraction f = a * B; Fraction g = a/B; cout <"a = 1/2" <endl <"B = 1/4" <endl <"a + B =" <c <endl <"- B = "<d <endl <" B-a = "<e <endl <" a * B = "<f <endl <" a/B = "<g <endl; fraction h; cin >>h; cout