Adding Input data validation to accept only integer values greater than 0

Question

Im simulating a vending machine and would like to set the product quantity text box to only accept values greater than 0. when i enter -1 my program accepts this value and displays it which i dont want.can someone help please

code is:

//create a new Employee object
    try // Exception handling to ensure that incorrect data type cannot be entered into text box creating a new product
       {
            Products newProd = new Products(this.textProdID.Text);
            newProd.ProductName= this.textProdName.Text;
            newProd.ProductQuantity= Convert.ToInt32(this.textProdQuantity.Text);
            newProd.ProductPrice= Convert.ToDouble(this.textProdPrice.Text);
            ProductList.Add(newProd);
            MessageBox.Show(newProd.ProdName + " has been added to the product list");
        }
     catch
     {
        MessageBox.Show("Format entered into text box Is incorrect please check and try again");
     }

Answer 1

You should add the Quantity range validation as per your specification - see the code snippet shown below:

//create a new Employee object
    try // Exception handling to ensure that incorrect data type cannot be entered into text box creating a new product
       {
            Products newProd = new Products(this.textProdID.Text);
            newProd.ProductName= this.textProdName.Text;
            newProd.ProductQuantity= Convert.ToInt32(this.textProdQuantity.Text);
            // add the input range validation 
            if (newProd.ProductQuantity<=0) throw new ArgumentException ("Quantity must be a positive number.");

            newProd.ProductPrice= Convert.ToDouble(this.textProdPrice.Text);
            ProductList.Add(newProd);
            MessageBox.Show(newProd.ProdName + " has been added to the product list");
        }
     catch
     {
        MessageBox.Show("Format entered into text box Is incorrect please check and try again");
     }

Another solution is just to show a MessageBox with error message if validation fail and return. Further performance optimization can be achieved by using TryParse() instead of Convert method, but considering relatively simple task, both solutions pertinent to this case will suffice the purpose. As a general recommendation, consider adding the input validation to the Control event (e.g. TextBox.TextChanged +=(s,e)=>{ // validation}; Also, pertinent to your case, consider setting the object to null in validation fail.

Hope this will help. Best regards,