C# How to loop user input until the datatype of the input is correct?

Question

How to make this piece of code loop asking for input from the user until int.TryParse()

is successful?

//setX
    public void setX()
    {
        //take the input from the user
        string temp;
        int temp2;
        System.Console.WriteLine("Enter a value for X:");
        temp = System.Console.ReadLine();
        if (int.TryParse(temp, out temp2))
            x = temp2;
        else
            System.Console.WriteLine("You must enter an integer type value"); 'need to make it ask user for another input if first one was of invalid type'
    }

Version of the code after the helpful answer:

 //setX
    public void setX()
    {
        //take the input from the user
        string temp;
        int temp2;
        System.Console.WriteLine("Enter a value for X:");
        temp = System.Console.ReadLine();
        if (int.TryParse(temp, out temp2))
            x = temp2;
        else
        {
            Console.WriteLine("The value must be of integer type");
            while (!int.TryParse(Console.ReadLine(), out temp2))
                Console.WriteLine("The value must be of integer type");
            x = temp2;
        }
    }

Lukáš Novotný · Accepted Answer · 2011-02-14 21:51:19Z

10

while (!int.TryParse(Console.ReadLine(), out mynum))
    Console.WriteLine("Try again");

edit:

public void setX() {
    Console.Write("Enter a value for X (int): ");
    while (!int.TryParse(Console.ReadLine(), out x))
        Console.Write("The value must be of integer type, try again: ");
}

Try this. I personally prefer to use while, but do .. while is also valid solution. The thing is that I don't really want to print error message before any input. However while has also problem with more complicated input that can't be pushed into one line. It really depends on what exactly you need. In some cases I'd even recommend to use goto even tho some people would probably track me down and slap me with a fish because of it.

edited Feb 14, 2011 at 21:51

answered Feb 14, 2011 at 20:15

Lukáš Novotný

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2 Comments

Bloodline Over a year ago

Thanks. I've edited my original post with the updated code. Is there a way to make this code shorter yet it would do the same thing? Just curious.

Lukáš Novotný Over a year ago

I've edited a little bit shorter solution of whole setX method for you

Marlon · Accepted Answer · 2011-02-14 20:38:49Z

4

Even though the question has been already marked as answered, do-while loops are much better for validating user input.

Notice your code:

Console.WriteLine("The value must be of integer type");
while (!int.TryParse(Console.ReadLine(), out temp2))
    Console.WriteLine("The value must be of integer type");

You have the same code at top and bottom. This can be changed:

do {
    Console.WriteLine("The value must be of integer type");
} while (!int.TryParse(Console.ReadLine(), out temp2));

answered Feb 14, 2011 at 20:38

Marlon

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1 Comment

Bloodline Over a year ago

Thanks. That's what I've been looking for.

Aman Jain · Accepted Answer · 2020-01-20 14:17:59Z

2

This can help too

public int fun()
{
    int Choice=0;
    try 
    {
        Choice = int.Parse(Console.ReadLine());
        return choice;
    } 
    catch (Exception) 
    {
        return fun(); 
    }
}

edited Jan 20, 2020 at 14:17

answered Jan 16, 2020 at 5:41

Aman Jain

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1 Comment

Eric J. Over a year ago

Don't use an exception for flow control in 2020 and beyond because int.TryParse() is available (and exceptions for flow control is an anti-pattern).

bhk · Accepted Answer · 2013-11-26 19:35:26Z

1

I've been wondering quite a lot, but I just figured it out!

    int number;
    bool check;
    do
    {
        Console.WriteLine("Enter an integer:");
        check = int.TryParse(Console.ReadLine(), out num1);
    }
    while (!check);

This code will loop until the user has entered an integer number. This way, the program doesn't simply report an error, but instead immediately allows the user to input again another, correct value.

answered Nov 26, 2013 at 19:35

bhk

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