Validating a specific string in C#

Question

  public bool IsOperator(TextBox textbox, string name)
        {
            if (name != "+" || name != "-" || name != "*" || name != "/")
            {
                MessageBox.Show(name + " Must be +, -, *, or /.", "Entry Error");
                txtOperator1.Focus();
                return false;
            }
            return true;
        }

I am making a basic calculator and I have to validate that the operand entered into the text box is either a +, -, *, or /. I coded this as a generic validating method have correctly called it in my program. However, when I run the program and enter any of the operands that should be valid it pops up and tells me they're not. I'm really stuck and would greatly appreciate any help.

Edit: Here is the other parts of my code that goes with this validation. The other validators are working fine it's just the IsOperator that is giving me grief.

private void btnCalculate_Click(object sender, EventArgs e)
        {
            
            try
            {
                if (IsValidData())
                {
                    decimal operand1 = Convert.ToDecimal(txtOperand1);
                    string operator1 = Convert.ToString(txtOperator1);
                    decimal operand2 = Convert.ToDecimal(txtOperand2);

                    decimal result = Calculate(operand1, operator1, operand2);

                    txtResult.Text = result.ToString("n4");
                    txtOperand1.Focus();
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message + "\n\n" + ex.GetType().ToString() + "\n" + ex.StackTrace, "Exception");
            }
        }

public bool IsValidData()
        {
            
                IsPresent(txtOperand1, "Operand 1") &&
                IsDecimal(txtOperand1, "Operand 1") &&
                IsWithinRange(txtOperand1, "Operand 1", 1, 999999) &&

                IsPresent(txtOperator1, "Operator") &&
                IsOperator(txtOperator1, "Operator") &&

                IsPresent(txtOperand2, "Operand 2") &&
                IsDecimal(txtOperand2, "Operand 2") &&
                IsWithinRange(txtOperand2, "Operand 2", 1, 999999);
        }

private decimal Calculate(decimal operand1, string operator1, decimal operand2)
        {
            //This method performs the calculation based on what operand was entered 
            if (txtOperator1.Text == "+")
            {
                decimal calculationResult =  operand1 + operand2;
                return calculationResult;
            }

            else if (txtOperator1.Text == "-")
            {
                decimal calculationResult = operand1 - operand2;
                return calculationResult;
            }

            else if (txtOperator1.Text == "*")
            {
                decimal calculationResult = operand1 * operand2;
                return calculationResult;
            }

            else 
            {
                decimal calculationResult = operand1 / operand2;
                return calculationResult;
            }
            
        }

This (name != "+" || name != "-" || name != "*" || name != "/") is always true — muglio
– muglio, Commented May 11, 2015 at 18:23

Khalid · Accepted Answer · 2015-05-12 19:51:52Z

2

You need to reverse your if statement logic

public bool IsOperator(TextBox textbox,string name)
    {
        if (textbox.Text== "+" || textbox.Text == "-" || textbox.Text == "*" || textbox.Text == "/")
        {
          return true;
        }
            MessageBox.Show(name + " Must be +, -, *, or /.", "Entry Error");
            txtOperator1.Focus();
            return false;            
    }

edited May 12, 2015 at 19:51

answered May 11, 2015 at 18:20

Khalid

2351 silver badge5 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Skyler Dyer Over a year ago

Thanks for the quick reply! It makes sense and I feel like it should work but for some reason it isn't :( This is how I called it in my IsValidData method if this helps. IsOperator(txtOperator1, "Operator") Let me know if posting any other parts of my code would help.

Khalid Over a year ago

Also try to setup a break-point on this function and check what is being passed to it.

Skyler Dyer Over a year ago

I edited the original post with the other parts of the code that I think are the relevant parts. Thanks again for the help.

Maantje · Accepted Answer · 2015-05-11 18:17:33Z

0

You are using || witch is Or so if it is not equal to + or - or * or / it will show you the message box. so if you do + it is not equal to - min so it will still show it.

answered May 11, 2015 at 18:17

Maantje

1,8012 gold badges22 silver badges33 bronze badges

Comments

Shar1er80 · Accepted Answer · 2015-05-11 18:30:36Z

You should use && (AND) instead of || (OR). When you're using || (OR), when one of those conditions is true, then the whole condition is true. So when name = "+", the first part of your if statement (name != "+") evaluates false, but all of the other parts evaluate true, and only one needs to evaluate true for the entire if statement to be true.

public bool IsOperator(TextBox textbox, string name)
{
    if (name != "+" && name != "-" && name != "*" && name != "/")
    {
        MessageBox.Show(name + " Must be +, -, *, or /.", "Entry Error");
        txtOperator1.Focus();
        return false;
    }
    return true;
}

Using the && (AND) operator, all conditions must be true for the whole condition to be true.

You could also try the following, which avoids using && (AND) and || (OR)...

private string validOperators = "+-*/";
public bool IsOperator(TextBox textbox, string name)
{
    if (!validOperator.Contains(name))
    {
        MessageBox.Show(name + " Must be +, -, *, or /.", "Entry Error");
        txtOperator1.Focus();
        return false;
    }
    return true;
}

Collectives™ on Stack Overflow

Validating a specific string in C#

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related