如何用自定义值作为局部变量名赋值？（禁用数组）

需要从文件读取内容转换为double类型，循环中通过counter拼接'a'的方式，将值分别存入a0、a1、a2、a3四个局部变量。尝试'a'+counter= SomethingDouble;报错，且作业禁止使用数组，寻求可行方案。

C++是静态类型语言，不支持在运行时动态生成局部变量名，你写的'a'+counter本质是计算ASCII码值，并非变量名，因此会报错。以下是几种符合要求的替代方案：

方案1：switch-case分支判断 #

直接根据counter的值分支赋值，逻辑清晰且完全符合作业要求：

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main() {
    fstream someFileStream;
    someFileStream.open("RandomFileName.txt");
    double a0, a1, a2, a3;
    string SomethingString;

    for (int counter = 0; counter <= 3; counter++) {
        getline(someFileStream, SomethingString);
        double SomethingDouble = stod(SomethingString);
        
        switch(counter) {
            case 0: a0 = SomethingDouble; break;
            case 1: a1 = SomethingDouble; break;
            case 2: a2 = SomethingDouble; break;
            case 3: a3 = SomethingDouble; break;
        }
    }
    someFileStream.close();

    // 可添加变量使用逻辑
    cout << a0 << " " << a1 << " " << a2 << " " << a3 << endl;
    return 0;
}

方案2：使用std::tuple封装变量 #

用tuple将四个double变量打包，通过索引完成赋值和取值，后续可直接提取为单独变量：

#include <iostream>
#include <fstream>
#include <string>
#include <tuple>

using namespace std;

int main() {
    fstream someFileStream;
    someFileStream.open("RandomFileName.txt");
    tuple<double, double, double, double> a_tuple;
    string SomethingString;

    for (int counter = 0; counter <= 3; counter++) {
        getline(someFileStream, SomethingString);
        double SomethingDouble = stod(SomethingString);
        
        switch(counter) {
            case 0: get<0>(a_tuple) = SomethingDouble; break;
            case 1: get<1>(a_tuple) = SomethingDouble; break;
            case 2: get<2>(a_tuple) = SomethingDouble; break;
            case 3: get<3>(a_tuple) = SomethingDouble; break;
        }
    }
    someFileStream.close();

    // 提取为单独变量使用
    double a0 = get<0>(a_tuple);
    double a1 = get<1>(a_tuple);
    double a2 = get<2>(a_tuple);
    double a3 = get<3>(a_tuple);
    cout << a0 << " " << a1 << " " << a2 << " " << a3 << endl;
    return 0;
}

方案3：指针数组指向已有变量 #

定义指针数组指向预先声明的a0-a3，通过指针完成赋值，规避“使用数组存储值”的限制：

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main() {
    fstream someFileStream;
    someFileStream.open("RandomFileName.txt");
    double a0, a1, a2, a3;
    double* vars[] = {&a0, &a1, &a2, &a3}; // 指针数组指向已有变量
    string SomethingString;

    for (int counter = 0; counter <= 3; counter++) {
        getline(someFileStream, SomethingString);
        double SomethingDouble = stod(SomethingString);
        *vars[counter] = SomethingDouble; // 通过指针赋值
    }
    someFileStream.close();

    cout << a0 << " " << a1 << " " << a2 << " " << a3 << endl;
    return 0;
}

内容的提问来源于stack exchange，提问作者Y K