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類型學(xué)轉(zhuǎn)換成其他類型有兩種方式:
一、用構(gòu)造函數(shù),將基本類型轉(zhuǎn)為構(gòu)造類型
1.用初始化的形式;
class X
{
public:
X(int n);
~X();
};
void f(X arg);
...
int main(){
X(3);
X=a;//a隱式調(diào)用構(gòu)造函數(shù)X(int n);
f(5);//把5調(diào)用構(gòu)造函數(shù)X(int n)轉(zhuǎn)為X arg.然后調(diào)用構(gòu)造函數(shù)。
return 0;
}
二、因?yàn)?span >帶參數(shù)的構(gòu)造函數(shù)無(wú)法將類類型轉(zhuǎn)為基本類型,所以設(shè)置類型轉(zhuǎn)換函數(shù)
#include<iostream>
using namespace std;
class rational
{
public:
rational();
rational(int n,int d=1);
rational(double x);//將double類型轉(zhuǎn)換成類類型。
operator double();//將類類型轉(zhuǎn)變?yōu)閐ouble類型,且注意其沒有返回值。
friend rational& operator+(const rational&, const rational&);
friend ostream & operator <<( ostream& os, const rational&);
//注意這里輸出類ostream前面不可以加const因?yàn)樵谳敵隽鹘?jīng)過os時(shí)會(huì)修改os
//且類型一定是引用類型因?yàn)楸仨氂胏out對(duì)象本身
~rational();
private:
int numerator;
int denominator;
};
int gcd(int a, int b);
rational::rational()
{
numerator = 0;
denominator = 0;
}
rational::rational(int n,int d){
int g;
if (d == 1){
numerator = n;
denominator = d;
}
else{
g = gcd(n, d);//求分子分母的最大公約數(shù)
numerator = n / g;//把分母化成最簡(jiǎn);
denominator = d / g;
}
}
rational::rational(double x){
int a, b, g;
a = int(x*1e5);//x乘10的5次方。把小數(shù)變成整數(shù)
b = int(1e5);
g = gcd(a, b);
numerator = a / g;
denominator = b / g;
}
rational::~rational()
{
}
rational::operator double(){//雖然沒有返回值依然要返回double類型的數(shù)。
return double(numerator) / double(denominator);
}
rational& operator +(const rational& a, const rational& b){
rational c;
int d = a.denominator*b.denominator;
int n = a.numerator*b.denominator + a.denominator*b.numerator;
int g = gcd(n, d);
c.denominator = d / g;//將分子分母化為最簡(jiǎn)
c.numerator = n / g;
return c;//返回類型是引用還是類類型都可以。
}
ostream& operator <<(ostream& os, const rational& a){
os << a.numerator;
if (a.denominator != 1){
os << "/" << a.denominator;
}
return os;//這里返回os類型的引用目的是連續(xù)使用cout<<"ss"<<"sss";
}
int gcd(int n, int d){//求最大公約數(shù)的算法
if (d == 0) return n;
else{
return gcd(d, n%d);
}
}
int main(){
rational a(2, 4);
rational b = 0.3;
rational c = a + b;
cout << double(a) << "+" << double(b)<<"="<<double(c)<<endl;
//將類類型對(duì)象a,b,c轉(zhuǎn)換成double類型。
cout << a << "+" << b << "=" << c << endl;
double x = b;
c = x + 1 + 0.6;
cout << x << "+" << 1 << "+" << 0.6 << "=" << c << endl;
cout << rational(x) << "+" << rational(1) << "+" << rational(0.6) << "=" << c << endl;
system("pause");
}
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