How to validate user input for whether it's an integer?

You were probably very close using TryParse, but I'm guessing you forgot the out keyword on the parameter:

int value;
if (int.TryParse(n, out value))
{

}

Just use this:

int i;
bool success = int.TryParse(n, out i);

if the parse was successful, success is true.

If that case i contain the number.

You probably got the out argument modifier wrong before. It has the out modifier to indicate that it is a value that gets initialized within the method called.

You can try with some simple regular expression :

  bool IsNumber(string text)
    {
      Regex regex = new Regex(@"^[-+]?[0-9]*\.?[0-9]+$");
      return regex.IsMatch(text);
    }

    private void SetNumber(string n)
    {
        int nVal = 0;

        if (int.TryParse(n, out nVal))
        {
            if (nVal < 0)
                number = Math.Abs(nVal);
            else
                number = nVal;
        }
        else
            number = 0;
    }

There are a lot of problems with this code:

• Using VB-style line comments (') instead of C# slashes
• Parse for integer returns an int and not a bool
• You should use TryParse with an out value
• h does not seem to be valid at all. Is it a type for n?
• There are variables that do not seem to be defined in function scope (number) are they defined at class scope?

But try this:

private void SetNumber(string n)
{
    int myInt;
    if (int.TryParse(n, out myInt)) //if user input is a number then
    {
        if (myInt < 0) //if user input is negative
            number = Math.Abs(n); //assign absolute version of user input
        else //else assign user input
            number = n;
    }
    else number = 0; //if user input is not an int then set number to 0
}

You could try something like below using int.TryParse..

        private void SetNumber(string n)
        {
            int parsed = -1;
            if (int.TryParse(n, out parsed)) //if user input is a number then
            ...

The reason there are complaints that it cannot convert an int to a bool is because the return type of int.Parse() is an int and not a bool and in c# conditionals need to evaluate bool values.

int.Parse will give you back an integer rather than a boolean.

You could use int.TryParse as you suggested.

int parsedValue;
if(int.TryParse(n, out parsedValue))
{
}

Well for one thing the inner if statement has an 'h' instead of an 'n' if(h < 0). But TryParse should work there assuming that 'number' is a class variable.

 private void SetNumber(string n)
    {
        int temp;
        bool success = Int32.TryParse(n, out temp);

        // If conversion successful
        if (success)
        {
            // If user input is negative
            if (temp < 0)
                number = Math.Abs(temp); // Assign absolute version of user input
            else // Assign user input
                number = temp;

        }
        else
        {
            number = 0;
        }

    }

int.Parse will convert a string to an integer. Current you have it within an if statement, so its treating the returned value of int.Parse as a bool, which its not.

Something like this will work:

private void SetNumber(string n)
{
    int num = 0;
    try{
        num = int.Parse(n);
        number = Math.Abs(num);
    }catch(Exception e){
        number = 0;
    }   
}

I did this in the simplest way I knew how.

 static void Main(string[] args)
    {
        string a, b;
        int f1, f2, x, y;
        Console.WriteLine("Enter two inputs");
        a = Convert.ToString(Console.ReadLine());
        b = Console.ReadLine();
        f1 = find(a);   
        f2 = find(b);   

        if (f1 == 0 && f2 == 0)
        {
            x = Convert.ToInt32(a);
            y = Convert.ToInt32(b);
            Console.WriteLine("Two inputs r number \n so tha additon of these text box is= " + (x + y).ToString());
        }
        else
            Console.WriteLine("One or tho inputs r string \n so tha concadination of these text box is = " + (a + b));
        Console.ReadKey();
    
    }
        static int find(string s)
        {
        string s1 = "";
        int f;
         for (int i = 0; i < s.Length; i++)
            for (int j = 0; j <= 9; j++)
            {
                string c = j.ToString();
                if (c[0] == s[i])
                {
                    s1 += c[0];
                }
            }
        
        if (s==s1)
            f= 0;
        else
            f= 1;

        return f;
    }