c# - How to read an int variable if it's an string

Question

I just encounter this in a test that said end the loop if the input is invalid then end the program. My code is like this

    int x=0;
    while(x!=(string)) // this is what I want to know what should i do here
  {
    Console.WriteLine("Input an integer: ");
    x = Int.Parse(Console.ReadLine);
  }
    Console.WriteLine("Invalid input");

What is the proper way to do this?
P.S.
That time, I don't know int.TryParse yet. So I'm exactly looking for a way without using int.TryParse

Answer 1

To me, this sounds like a job for a do-while loop with an int.tryparse.

A simple code example of this is as follows:

        string input = string.Empty;

        int x = 0;
        do
        {
            input = Console.ReadLine();
        } while (int.TryParse(input, out x));

        Console.WriteLine("Invalid entry");

        Console.ReadKey();

Do While works similar to a while loop, but it leaves the conditional to the end, which allows for a tryparse at the end.

Tryparse returns a boolean value of true when the value can be successfully parsed as an integer, otherwise, returning false and ending the loop.

Answer 2

If you just want to read a string, try to convert to an integer, and exit the program if it's not a valid integer, then you'd use int.TryParse, like this:

string input = Console.ReadLine();
if (int.TryParse(input, out x))
{
    // do something with x
}
else
{
    // input was invalid.
}

If you want to continue doing this in a loop until you got invalid input:

bool validInput = true;
while (validInput == true)
{
    string input = Console.ReadLine();
    int x;
    if (int.TryParse(input, out x))
    {
        Console.WriteLine(x);  // output the integer
    }
    else
    {
        Console.WriteLine("Input was not an integer");
        validInput = false;
    }
}

Update

What, exactly, does your test consider "an integer?" Is it just a string that consists only of one or more digits in the set [0-9]? Or does it need to fit within the C# language's definition of Int32? If the former, then you can use a regular expression to determine if the string is just digits. Otherwise, int.TryParse or int.Parse wrapped in a try ... catch is the way you'll have to do it.

Answer 3

try this:

         Console.WriteLine("About to call Console.ReadLine in a loop.");
        Console.WriteLine("----");
        String s;

        do
        {

            s = Console.ReadLine();
            Regex regex = new Regex("[0-9]");
            Regex regex2 = new Regex("[a-zA-Z]");
            if (regex.IsMatch(s))
            {
                if (regex.IsMatch(s) && regex2.IsMatch(s))
                {
                    Console.WriteLine("You entered an combination of number and String = " + s.ToString());
                }
                else
                {
                    int cnt = s.Count(x => x == '.');
                    if (s.Count(x => x == '.') > 1)
                    {
                        Console.WriteLine("Invalid input of number = " + s.ToString());
                    }
                    else if (s.Count(x => x == '.') == 1 && regex.IsMatch(s))
                    {
                        Console.WriteLine("You entered a decimal number = " + s.ToString());
                    }

                    else
                    {
                        char[] str = "!@#$%^&*()',-./:;<=>?@_`{|}~¡¢£¤¥¦§¨©¬®¯°±²³´µ¶¸¹º»¼½¾¿ÀÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöL÷øùúûüýþÿ\"".ToArray();
                        int indexOf = s.IndexOfAny(str);

                        if (indexOf == -1)
                        {

                            Console.WriteLine("You entered a number = " + s.ToString());

                        }
                        else
                        {
                            Console.WriteLine("You entered an combination of number and String = " + s.ToString());
                        }

                    }

                }
            }
            else
            {
                if (s.Trim().Length < 1)
                {
                    Console.WriteLine("Please enter any value.");
                }
                else
                {
                    Console.WriteLine("You entered a String = " + s.ToString());
                }

            }


        } while (s != null);
        Console.WriteLine("---");

Answer 4

You define X as a int first and the X will always be int-type (),Unless you convert this int type,i think use try{...} catch{...} may be a good way to solve this:

string x;
int result;
while (true)
{
    x = Console.ReadLine();
    try
    {
        result = int.Parse(x);
        Console.WriteLine("int input");
    }
    catch
    {
        Console.WriteLine("Invalid input ");
    }
}

or you can use regular expression like this:

var reg = new Regex("^-?\\d+$");
string result;
Match m;
for (;;)
{
    result = Console.ReadLine();
    m = reg.Match(result);
    if(m.Success)
    {
        Console.WriteLine("int input");
    }
    else
    {
        Console.WriteLine("Invalid input: ");
    }
}