"No overload for method 'TryParse' takes one argument" error when using double.TryParse

c#

Solution

            double rad = Convert.ToDouble(radius);

            if (double.TryParse(rad) == false)

should be

            double rad;
            if (!double.TryParse(radius, out rad))

Use `!` (not) instead of `== false` just as better coding practice.

Also, TryParse needs an `out` value (It does the parsing, no need for `Convert.ToDouble` and ... your `Convert.ToDouble` will error if it's not parseable - bad!)

Problem

Level:Novice I'm writing a console program in C# that finds the area of circles, triangles, and trapezoids. I want to make sure the user only enters numbers, by using double.TryParse. Here's the code: ``` Console.WriteLine("AreaSolution finds the area of different shapes."); Console.ReadLine(); ln1: Console.WriteLine("To find area of circle, press c. To find area of triangle press t.For trapezoid, enter tr. "); var x = Console.ReadLine(); switch (x) { case "c": Console.WriteLine("Enter radius of circle, in centimeters"); var radius = Console.ReadLine(); double rad = Convert.ToDouble(radius); if (double.TryParse(rad) == false) { Console.WriteLine("Numbers only!"); }; Console.WriteLine("AREA: " + 3.14 * rad * rad + " cm sq."); Console.ReadLine(); break; case "t": Console.WriteLine("Enter base, in centimeters"); var bas = Console.ReadLine(); double tbase = Convert.ToDouble(bas); Console.WriteLine("Enter height, in centimeters"); var tHi = Console.ReadLine(); double tHei = Convert.ToDouble(tHi); Console.WriteLine("AREA: " + (tbase * tHei / 2) + " cm sq."); Console.ReadLine(); break; case "tr": Console.WriteLine("Enter the length of the top base, in cm"); var tpbas = Console.ReadLine(); double bas1 = Convert.ToDouble(tpbas); Console.WriteLine("Enter length of bottom base, in cm"); var btmbase = Console.ReadLine(); double bas2 = Convert.ToDouble(btmbase); Console.WriteLine("Enter height, in cm"); var trHe = Console.ReadLine(); double trH = Convert.ToDouble(trHe); Console.WriteLine("AREA: " + (bas1 + bas2) * trH / 2 + " cm sq."); Console.ReadLine(); break; default: Console.WriteLine("Please enter a valid character: c for circle, t for triangle, or tr for trapeziod."); break; } Console.WriteLine("Another computation?(Y/N)"); string newComp = Console.ReadLine(); switch (newComp) { case "y": goto ln1; break; case "n": return; break; } ``` However, on the line of "double.TryParse(rad)", I get an error: No overload for method 'TryParse' takes one argument. How can I fix this error? Thanks in advance. Your help is greatly appreciated.

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