using System;
using System.Globalization;

//to Int
var strNumber = "42";
//the first method
int number1 = int.Parse(strNumber);
//the second method
int number2 = Convert.ToInt32(strNumber);

//to Double and Float
//the first method
var strPi = "3.14";
float pi = float.Parse(strPi);

//the second method
var strExp = "2.71828";
var exp = Convert.ToDouble(strExp);

//the third method
var strHalf = "0,5";
var formatter = new CultureInfo("en") {
    NumberFormat = {NumberDecimalSeparator = ","}
};
var half = Convert.ToDouble(strHalf, formatter);

Console.WriteLine(number1);
Console.WriteLine(number2);
Console.WriteLine(pi);
Console.WriteLine(exp);
Console.WriteLine(half);