如何将字符串转换为变量,vb6/c#/ c ++？

Dim str As String
Dim num As Integer

str = "10"
num = Eval(str)

using System;

class Program
{
    static void Main()
    {
        string str = "10";
        Type type = Type.GetType("System.Int32");
        object num = Convert.ChangeType(str, type);
        Console.WriteLine(num);
    }
}

#include<iostream>
#include<boost/lexical_cast.hpp>

int main()
{
    std::string str = "10";
    int num = boost::lexical_cast<int>(str);
    std::cout<< num<< std::endl;
    return 0;
}