C++ 将字符串数组中的字符转换为浮点

我正在做一个项目，它接受坐标用户的字符串输入。 输入示例：

"Polygons = [(1, 1), (4, 1), (4, 5), (3,5), (1, 5); (5,3), (3, 4), (6, 4), (6, 12), (3, 12)]"

我正在做的一个函数是检查最小/最大X，它显然是a之后的任何数字，但是困扰我的问题是将a之后的数字转换为浮点，以便在计算和数字比较中使用它

    #include <iostream>
    #include "string"
    #include <stdlib.h>
    #include <cstdlib>
    using namespace std;
    //Using a constant string for testing
    string Polygon_Input = "Polygons = [(1, 1), (4, 1), (4, 5), (3,5), (1, 5); (5,3), (3, 4), (6, 4), (6, 12), (3, 12)]"; 
    string Operation;
    float Min_X = 9999;
    int main()
    {

        getline(cin, Operation);

        if (Operation == "Minimum_X")
        {
            for (int i; i <= Polygon_Input.length(); i++)
            {
                if (Polygon_Input[i] == '(')
                {

                   float X = Polygon_Input[i + 1];
                   if (X < Min_X)
                   {
                       Min_X = X;
                   }

                }

            }
            cout << Min_X;
        }

这不起作用，它总是以Min_X的形式输出49

我也尝试过同样的代码，只做了一次修改，但仍然不起作用

    if (Polygon_Input[i] == '(')
    {

        string X_As_String = Polygon_Input.substr(i + 1, i + 1);
        float X = atof(X_As_String.c_str());
       if (X < Min_X)
       {
           Min_X = X;
       }

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首先，代码中有几个问题

浮动最小值X=9999

最小值必须在列表中。将第一个元素初始化为最小值，并将其与其余元素进行比较

如果X 值X是int，而Min_X是float。不要将int与float进行比较。如果需要整数，则将两者声明为float，然后强制转换

---

对于int i=0；i由于所有x都大于0，并且您将Min_x初始化为0，因此您的x//#include <limits> // no need for this #include <iostream> #include <string> #include <cstdlib> #include <cstdlib> using namespace std; //Using a constant string for testing string Polygon_Input = "Polygons = [(1, 1), (4, 1), (4, 5), (3,5), (1, 5); (5,3), (3, 4), (6, 4), (6, 12), (3, 12)]"; string Operation("Minimum_X"); //float Min_X = 9999; ?????? Why float Min_X; bool flag(true); int main() { //getline(cin, Operation); // commented out for test if (Operation == "Minimum_X") { for (int i=0; i < Polygon_Input.size(); i++) { if ( Polygon_Input[i] == '(' ) { // extract X values (i.e. the first co-ordinate of a point ) std::string temp = Polygon_Input.substr(i+1, Polygon_Input.find_first_of(",",i)-i-1 ); // convert strig to float float X = std::stof(temp); // store first element and compare it with the rest if(flag){ Min_X = X; flag=false; } // int X = Polygon_Input[i + 1] - '0'; ????? What is this? if (X < Min_X) { Min_X = X; } } } cout << Min_X << endl; } return 0; }