简单工厂模式

C++版本

参考：https://www.cnblogs.com/Galesaur-wcy/p/15926669.html

#include <iostream>
using namespace std;
// 运算类
class Operation
{
private:double _NumA;double _NumB;public:void SetNumA(){cout << "Enter a double number: ";if (!(cin >> _NumA))throw "It must be a number";}double GetNumA(){return _NumA;}void SetNumB(){cout << "Enter a double number: ";if (!(cin >> _NumB))throw "It must be a number";}double GetNumB(){return _NumB;}virtual double GetResult(){int result = 0;return result;}
};class OperationAdd : public Operation
{
public:double GetResult(){double result = GetNumA() + GetNumB();return result;}
};class OperationSub : public Operation
{
public:double GetResult(){double result = GetNumA() - GetNumB();return result;}
};class OperationMul : public Operation
{
public:double GetResult(){double result = GetNumA() * GetNumB();return result;}
};class OperationDiv : public Operation
{
public:double GetResult(){if (GetNumB() == 0){throw "The divisor cannot be 0";}double result = GetNumA() / GetNumB();return result;}
};class OperatorFactory
{
public:Operation *CreatOperation(char s){Operation *ope = nullptr;switch (s){case '+':ope = new OperationAdd;break;case '-':ope = new OperationSub;break;case '*':ope = new OperationMul;break;case '/':ope = new OperationDiv;break;default:throw "Error input operator!";break;}return ope;}
};int main()
{OperatorFactory fac;cout << "Choose an operation:";char operator_char;cin >> operator_char;try{Operation *oper = fac.CreatOperation(operator_char);oper->SetNumA();oper->SetNumB();cout << "result is: " << oper->GetResult() << endl;}catch (const char *err){cerr << err << endl;return -1;}return 0;
}

C版本

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>typedef struct Operation
{double NumA;double NumB;double (*GetResult)(struct Operation *);
} Operation;typedef struct OperationAdd
{Operation base; // 设置为第一个成员属性，模拟继承
} OperationAdd;typedef struct OperationSub
{Operation base;
} OperationSub;typedef struct OperationMul
{Operation base;
} OperationMul;typedef struct OperationDiv
{Operation base;
} OperationDiv;double OperationAddGetResult(struct Operation *op)
{OperationAdd *add = (OperationAdd *)op;return add->base.NumA + add->base.NumB;
}double OperationSubGetResult(struct Operation *op)
{OperationSub *sub = (OperationSub *)op;return sub->base.NumA - sub->base.NumB;
}double OperationMulGetResult(struct Operation *op)
{OperationMul *mul = (OperationMul *)op;return mul->base.NumA * mul->base.NumB;
}double OperationDivGetResult(struct Operation *op)
{OperationDiv *div = (OperationDiv *)op;if (div->base.NumB == 0){fputs("The divisor cannot be 0\n", stderr);exit(EXIT_FAILURE);}return div->base.NumA / div->base.NumB;
}Operation *CreateOperation(char op)
{Operation *ope = NULL;switch (op){case '+':ope = malloc(sizeof(OperationAdd));ope->GetResult = OperationAddGetResult;break;case '-':ope = malloc(sizeof(OperationSub));ope->GetResult = OperationSubGetResult;break;case '*':ope = malloc(sizeof(OperationMul));ope->GetResult = OperationMulGetResult;break;case '/':ope = malloc(sizeof(OperationDiv));ope->GetResult = OperationDivGetResult;break;default:fputs("Error input operator!\n", stderr);return NULL;}return ope;
}void SetNumA(Operation *ope)
{printf("Enter a double number: ");if (scanf("%lf", &ope->NumA) != 1){fputs("It must be a number\n", stderr);exit(EXIT_FAILURE);}
}void SetNumB(Operation *ope)
{printf("Enter a double number: ");if (scanf("%lf", &ope->NumB) != 1){fputs("It must be a number\n", stderr);exit(EXIT_FAILURE);}
}int main()
{printf("Choose an operation: ");char operator_char = getchar();Operation *oper = CreateOperation(operator_char);if (!oper)return EXIT_FAILURE;SetNumA(oper);SetNumB(oper);printf("Result is: %f\n", oper->GetResult(oper));free(oper);return 0;
}