原文：
https://www.cnblogs.com/tanrong/p/7074253.html
string s = “123.2”;
//方法1
float f1 = Convert.ToSingle(s);
//方法2
float f2;
if (!float.TryParse(s, out f2))
{
Console.WriteLine(“无法转换！”);
}
float volume = 0.5F; //double 转float