Change the amount of times code checks number

Question

            Console.Write("Enter -");
            string input = Convert.ToString(Console.ReadLine());
            string ascii = input;
            byte[] ASCIIValues = Encoding.ASCII.GetBytes(ascii);
            for (int i = 0; i < input.Length; i++)
            {
                if (ASCIIValues[i] >= 48 && ASCIIValues[i] <= 57)
                {
                    Console.WriteLine("Is number");
                }
                else
                {
                    Console.WriteLine("Is not number");
                }
            } 

I have made a code where it checks if you have entered number or not. It works fine while using only numbers from 1 to 9 . When I enter number with more digits the code checks each number. For example I enter 100 , and the code shows 3 lines "Is number." How could I change it , to only showing 1 line of "Is number."

Answer 1

Thats very complicated code for such a simple task

        Console.Write("Enter -");
        string input = Console.ReadLine();
        if(input.All(c=>Char.IsDigit(c)))
             Console.WriteLine("Is number");
        else
             Console.WriteLine("Is not a number");

or you could do this (since the next thing I expect you to do is convert that input to a number)

        Console.Write("Enter -");
        string input = Console.ReadLine();
        int num;
        if (Int32.TryParse(input, out num))
            Console.WriteLine("is a number");
        else
            Console.WriteLine("is not a number");

TryParse tries to convert the string to a number and reports success or failure

Answer 2

You are reading each char in the whole string and printing the result for each char... To follow your approach you should be checking the whole string first and print a positive result only if all char check was verified as a number.

Try something like this:

// ... your previous code
bool result = true;
for (int i = 0; i < input.Length; i++)
    if (ASCIIValues[i] >= 48 && ASCIIValues[i] <= 57)
        continue;
    else
    {
        result = false;
        break;
    }

if (result == true)
    Console.WriteLine("Is number");
else
    Console.WriteLine("Is not number");

Here I'm initializing a bool variable result with true value. If the code runs until the end of the loop with no break call, it would be considered a number. Otherwise, it would be false

Note: the char.IsNumber(char inputChar) function is a System's library function that does something like what you did with ASCII code checks. Using it, your code should look like this:

public static bool IsNumeric(string input)
{
    if(input.Length == 0)
        return false;
    
    for(int i = 0; i <input.Length; i++)
        if(!char.IsNumber(input[i]))
            return false;
           
    return true;
}