using System;

namespace ConsoleApp1 { class program { public static void Main() { int qty; double price;

        Console.WriteLine("please enter the qty");
        qty = Convert.ToInt32(Console.ReadLine());
        Console.WriteLine("please enter the price ");
        price = Convert.ToDouble(Console.ReadLine());

        double total = price * qty;
        Console.WriteLine($"tota is : {total:c}");

        Console.ReadKey();  
    }
}

}

output

please enter the qty

3

please enter the price

12.44

error message after entering double: 12.44

Unhandled exception. System.FormatException: Input string was not in a correct format. at System.Number.ThrowOverflowOrFormatException(ParsingStatus status, TypeCode type) at System.Convert.ToDouble(String value) at ConsoleApp1.program.Main() in C:\Users\Baba\Desktop\C#\ConsoleApp1\ConsoleApp1\Program.cs:line 14

CodePudding user response：

Welcome to SO! In addition to @PaulSinnema 's input: you could try TryParse() to detect/ avoid invalid user input:

using System;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            //int qty;
            //double price;

            Console.WriteLine("please enter the qty");
            //qty = Convert.ToInt32(Console.ReadLine());
            var input = Console.ReadLine();
            if (!Int32.TryParse(input, out int qty))
            {
                Console.WriteLine($"invalid input \"{input}\"");
                Console.ReadKey();
                return;
            }

            Console.WriteLine("please enter the price ");
            //price = Convert.ToDouble(input);
            input = Console.ReadLine();
            if (!double.TryParse(input, out double price))
            {
                Console.WriteLine($"invalid input \"{input}\"");
                Console.ReadKey();
                return;
            }

            double total = price * qty;
            Console.WriteLine($"total is : {total:c}");

            Console.ReadKey();
        }
    }
}