面向对象得编程思想：通过封装、继承、多态把程序的耦合度降低，用设计模式使得程序更加的灵活、容易修改并且易于复用；
复用：让业务逻辑和界面逻辑分开，让它们之间的耦合度下降，只有这样才能达到易于维护或扩展。
继承和多态：降低耦合性，让原有已经编译好的程序不参与功能添加中，增加新功能不需要原有算法运算类参与。
版本1：功能实现
版本1：功能实现
class Program {
public:
double str2double(char* str) {
return atof(str);
}
void cal(void) {
try {
cout << "请输入数字A: " << endl;
cin >> strNumberA;
cout << "请选择运算符号(+、-、*、\) " << endl;
cin >> strOperate;
cout << "请输入数字B: " << endl;
cin >> strNumberB;
switch (strOperate)
{
case '+':
result = str2double(&strNumberA[0]) + str2double(&strNumberB[0]); break;
case '-':
result = str2double(&strNumberA[0]) - str2double(&strNumberB[0]); break;
case '*':
result = str2double(&strNumberA[0]) * str2double(&strNumberB[0]); break;
case '/':
if (strNumberB == "0") {
throw runtime_error("除数不能为0");
}
result = str2double(&strNumberA[0]) / str2double(&strNumberB[0]); break;
default:
break;
}
cout << "结果是: " << result <<endl;
}
catch (runtime_error err) {
cout << err.what() << endl;
}
}
private:
string strNumberA, strNumberB;
double result;
char strOperate;
};
int main(int argc,char** argv)
{
Program myprogram;
myprogram.cal();
return 0;
}版本2：业务封装
让业务逻辑和界面逻辑分开
class Operation {
public:
static double GetResult(double NumberA, double NumberB,char strOperate){
double result=0.0f;
switch (strOperate)
{
case '+':
result = NumberA + NumberB; break;
case '-':
result = NumberA - NumberB; break;
case '*':
result = NumberA * NumberB; break;
case '/':
result = NumberA / NumberB; break;
default:
break;
}
return result;
}
};
class Program {
public:
double str2double(char* str) {
return atof(str);
}
void cal(void) {
try {
cout << "请输入数字A: " << endl;
cin >> strNumberA;
cout << "请选择运算符号(+、-、*、\) " << endl;
cin >> strOperate;
cout << "请输入数字B: " << endl;
cin >> strNumberB;
if (strNumberB == "0" && strOperate=='/') {
throw runtime_error("除数不能为0");
}
result = Operation::GetResult(str2double(&strNumberA[0]), str2double(&strNumberB[0]), strOperate);
cout << "结果是: " << result << endl;
}
catch (runtime_error err) {
cout << err.what() << endl;
}
}
private:
string strNumberA, strNumberB;
double result;
char strOperate;
};
int main(int argc,char** argv)
{
Program myprogram;
myprogram.cal();
return 0;
}版本3：低耦合
继承和多态：若要添加新功能(平方根、立方根、自然对数、正余弦)只需要增加相应的运算子类，同时修改运算类工厂。
class Operation {
public:
virtual double GetResult() {
double result = 0.0f;
return result;
}
double getA() {
return NumberA;
}
double getB() {
return NumberB;
}
void setA(double var) {
NumberA = var;
}
void setB(double var) {
NumberB = var;
}
protected:
double NumberA;
double NumberB;
};
class OperationAdd:public Operation {
public: // 加法运算类
double GetResult() {
return NumberA + NumberB;
}
};
class OperationSub :public Operation {
public: // 减法运算类
double GetResult() {
return NumberA - NumberB;
}
};
class OperationMul :public Operation {
public: // 乘法运算类
double GetResult() {
return NumberA * NumberB;
}
};
class OperationDiv :public Operation {
public: // 除法运算类
double GetResult() {
try {
if (NumberB == 0)
throw runtime_error("除数不能为0");
return NumberA / NumberB;
}
catch (runtime_error err) {
cout << err.what() << endl;
}
return 0;
}
};
class OperationFactory {
public: // 运算类工厂
static Operation* createOperate(char operate) {
Operation *oper=NULL;
switch (operate)
{
case '+':
oper = new OperationAdd; break;
case '-':
oper = new OperationSub; break;
case '*':
oper = new OperationMul; break;
case '/':
oper = new OperationDiv; break;
default:
break;
}
return oper;
}
};
class Program {
public:
double str2double(char* str) {
return atof(str);
}
void cal(void) {
try {
cout << "请输入数字A: " << endl;
cin >> strNumberA;
cout << "请选择运算符号(+、-、*、\) " << endl;
cin >> strOperate;
cout << "请输入数字B: " << endl;
cin >> strNumberB;
if (strNumberB == "0" && strOperate=='/') {
throw runtime_error("除数不能为0");
}
// result = Operation::GetResult(str2double(&strNumberA[0]), str2double(&strNumberB[0]), strOperate);
cout << "结果是: " << result << endl;
}
catch (runtime_error err) {
cout << err.what() << endl;
}
}
private:
string strNumberA, strNumberB;
double result;
char strOperate;
};
int main(int argc,char** argv)
{
Operation *oper=NULL;
oper = OperationFactory::createOperate('/');
oper->setA(10);
oper->setB(20);
double result = oper->GetResult();
return 0;
}
