public static bool isPrime(int number)
{

for (int i = 2; i < number; i++)
{
if (number % i == 0)
{
return false;
}
}

return true;
}

public int secret(int x)
{
if ((x < 100) && isPrime(x))
return (x);
else return (0);
}

private void button1_Click(object sender, EventArgs e)
{
int val1=secret(Convert.ToInt32(textBox1.Text));
int val2 = secret(Convert.ToInt32(textBox2.Text));

if (val1 == 0 || val2 == 0)
{
label1.Text = "Prime number and between 0 to 100 please";
return;
}

int final = Convert.ToInt32(textBox1.Text) + Convert.ToInt32(textBox2.Text);
int val3 = secret(final);
if (val3 == val1 + val2)
{
label1.Text = "Perfect!!!";
}

}