Question

When I try to enter the quit string, xxx, why does it throw an exception? It works in a while loop, but not with do…while loop.

After I convert to integer, the string variable only lets me use numeric characters (like -999) to exit the do…while loop. But I want to make the loop control variable a word like “quit” and not numbers. How can I do that?

Here is my code.

using System;
namespace StringInputPractice
{
    class StringInputPractice
    {
        static void Main()
        {
            // Declarations

            string inValue;
            int first;
            int second;
            int sum;

            do
            {
                Console.Write("\nEnter the first number. (Type \"xxx\" to exit):   ");
                inValue = Console.ReadLine();

                first = Convert.ToInt32(inValue);   //@@@@@
                Console.Write("\nEnter the second number. (Type \"xxx\" to exit):   ");
                inValue = Console.ReadLine();
                second = int.Parse(inValue);

                sum = first + second;

                Console.WriteLine("\nThe sum of {0} and {1} is {2}.", first,
                    second, sum);

                /* Things I've tried inside do { } and that don't work */

                //inValue = "";
                //inValue = null;
                //inValue = inValue.ToString();
                //inValue = first.ToString();
                //inValue = second.ToString();
            }

            while (inValue != "xxx");   /*If you enter a non-numeric string,
                                         * an exception is thrown at
                                         * @@@@@ above.
                                         */

            Console.ReadLine();
        }
    }
}

Answer 1

Try this: use int.TryParse instead of Convert.ToInt32

public void myfun()
        {
            string inValue;
            int first;
            int second;
            int sum;

            do
            {
                Console.Write("\nEnter the first number. (Type \"xxx\" to exit):   ");
                inValue = Console.ReadLine();

                if (int.TryParse(inValue, out first))
                {
                   // first = Convert.ToInt32(inValue);   //@@@@@
                    Console.Write("\nEnter the second number. (Type \"xxx\" to exit):   ");
                    inValue = Console.ReadLine();
                    if(int.TryParse(inValue, out second))
                    {
                   // second = int.Parse(inValue);

                    sum = first + second;

                    Console.WriteLine("\nThe sum of {0} and {1} is {2}.", first,
                        second, sum);
                    }
                }
                /* Things I've tried inside do { } and that don't work */

                //inValue = "";
                //inValue = null;
                //inValue = inValue.ToString();
                //inValue = first.ToString();
                //inValue = second.ToString();
            }

            while (inValue != "xxx");   /*If you enter a non-numeric string,
                                     * an exception is thrown at
                                     * @@@@@ above.
                                     */

            Console.ReadLine();
        }