[Solved] C# while loop not functioning [closed]

You need to split it up into sections.

First: Get positive number

double i;
double k;

Console.Write("What is your total income : ");

while (!double.TryParse(Console.ReadLine(), out i) || i < 0)
{
    if (i < 0)
    {
        Console.WriteLine("Your income cannot be negative.");
    }
    else 
    {
        Console.WriteLine("Enter your income as a whole-dollar numeric figure.");
    }
}

Second: Get number of children

Console.Write("How many children do you have: ");

while (!double.TryParse(Console.ReadLine(), out k) || k < 0)
{
    if (k < 0)
    {
        Console.WriteLine("You must enter a positive number.");
    }
    else 
    {
        Console.WriteLine("You must enter a valid number.");
    }
}

Third: Calculate

double totalTax = (i - 10000 - (k * 2000)) * 0.02;

if (totalTax <= 10000)
{
    Console.WriteLine("You owe no tax.");
    Console.WriteLine("\n\n Hit Enter to exit.");
    Console.ReadLine();
}
else
{
    Console.WriteLine("You owe a total of $ " + totalTax + " tax.");
    Console.WriteLine("\n\n Hit Enter to exit.");
    Console.ReadLine();
}

Whenever you get a wrong input, the while loop forces you to stay inside. When you get out, you can be sure the input is correct.

PS: I would use int for number of children, because it doesn’t make any sense that you would have 2.3 children.