c++ - 我将如何清理这些If语句？

Question

if (calculation == "help") {
    cout << "add, subtract, multiplication, divide\nsquare root, sin, cos, power\n";
}
else if (calculation == "add") {
    cout << num1 << " + " << num2 << " = " << num1 + num2 << endl;
}
else if (calculation == "subtract") {
    cout << num1 << " - " << num2 << " = " << num1 - num2 << endl;
}
else if (calculation == "multiplication") {
    cout << num1 << " x " << num2 << " = " << num1 * num2 << endl;
}
else if (calculation == "divide") {
    cout << num1 << " / " << num2 << " = " << num1/ num2 << endl;
}
else if (calculation == "square root") {
    cout << "The square root of the first number is " << sqrt(num1) << ". The square root of the second number is " << sqrt(num2) << "." << endl;
}
else if (calculation == "sin") {
    cout << "The sine of the first number is " << sin(num1) << ". The sine of the second number is " << sin(num2) << "." << endl;
}
else if (calculation == "cos") {
    cout << "The cosine of the first number is " << cos(num1) << ". The cosine of the second number is " << cos(num2) << "." << endl;
}
else if (calculation == "power") {
    cout << num1 << " to the power of " << num2 << " = " << pow(num1, num2) << endl;
}

我有一个解决这些if语句的想法，例如创建 map 或字典。我不相信您也不能在C++中将字符串与switch语句一起使用。任何帮助深表感谢!

编辑:我能够使用 map 。

map<string, int> Choices = {
        { "help", 0 },
        { "add", 1 },
        { "subtract", 2 },
        { "multiply", 3 },
        { "divide", 4 },
        { "square root", 5 },
        { "sine", 6 },
        { "cosine", 7 },
        { "power", 8 }
        };

    it = Choices.find(choice);
    i = it->second;

如果有更快的方法，请告诉我。感谢您的所有回复!

Answer 1

如果您匹配前两个字符并将其转换为数字，则可以创建一个开关。它不会很漂亮，但是会很快

编辑:如果字符串的第一部分是唯一的，我就如何使用“字符串”创建开关做了一个示例。如果需要，可以用两个以上的字符来完成，如果有重复，可以用大写字母进行切换。

仅在性能非常重要的情况下执行此操作，否则它将破坏其他解决方案的速度

#include <iostream>
#include <string>

int main()
{
    // first some code to show how to calculate constant from string if the first part in string is unique
    unsigned int uNumber = (unsigned int)'A';
    std::cout << uNumber << std::endl;
    uNumber <<= 8;
    std::cout << uNumber << std::endl;
    uNumber += (unsigned int)'A';
    std::cout << uNumber << std::endl;

    unsigned int uNumberAA = (unsigned int)*(uint16_t*)"AA";
    std::cout << uNumberAA << std::endl;
    uNumberAA = (unsigned int)*(uint16_t*)"AAAA";
    std::cout << uNumberAA << std::endl;


    // How to create a switch with strings

    static constexpr unsigned int he_help = ((unsigned int)'h' << 8) + (unsigned int)'e';           // "help"
    static constexpr unsigned int ad_add = ((unsigned int)'a' << 8) + (unsigned int)'d';            // "add"
    static constexpr unsigned int su_subtract = ((unsigned int)'s' << 8) + (unsigned int)'u';       // "subtract"
    static constexpr unsigned int mu_multiplication = ((unsigned int)'m' << 8) + (unsigned int)'u'; // "multiplication"

    std::string calculation = "subtract";

    uNumber = ((unsigned int)calculation[0] << 8) + (unsigned int)calculation[1];
    switch(uNumber)
    {
    case he_help :
        std::cout << "help" << std::endl;
        break;
    case ad_add :
        std::cout << "add" << std::endl;
        break;
    case su_subtract :
        std::cout << "subtract" << std::endl;
        break;
    case mu_multiplication :
        std::cout << "multiplication" << std::endl;
        break;
    }
}