Validate number input on text boxes [closed]

I would consider something like:

 //make sure that we have a valid number in the text box with no other characters //loop through the string, examining each character for (int i = 0; i < txtHour.Text.Length; i++) { //if this character isn't a number, then don't close the form or continue if (!char.IsNumber(txtHour.Text[i])) { MessageBox.Show("Value for 'txtHour' must be a number from 1 to 24"); return; } } //now that we know we have a valid number, convert the string to int and make sure it's not less than 1 or greater than 24 int testInt = Convert.ToInt32(txtHour.Text); if (testInt < 1 || testInt > 24) { MessageBox.Show("Value for 'txtHour' must be a number from 1 to 24"); return; } 

For the method example that you asked for in your comment you could do something more like:

 ////////////////////////////////////////////////////////////////////// //in your main code: if (!isValidHour(textBox1.Text)) MessageBox.Show("Value for field must be a number from 1 to 24"); if (!isValidHour(textBox2.Text)) MessageBox.Show("Value for field must be a number from 1 to 24"); ////////////////////////////////////////////////////////////////////// ///method to validate if text field is an INT from 1 to 24 bool isValidHour (string stringToValidate) { //make sure that we have a valid number in the text box with no other characters //loop through the string, examining each character for (int i = 0; i < stringToValidate.Length; i++) { //if this character isn't a number, then don't close the form or continue if (!char.IsNumber(stringToValidate[i])) { //MessageBox.Show("Value for 'txtHour' must be a number from 1 to 24"); return false; } } //now that we know we have a valid number, convert the string to int and make sure it's not less than 1 or greater than 24 int testInt = Convert.ToInt32(stringToValidate); if (testInt < 1 || testInt > 24) { //MessageBox.Show("Value for 'txtHour' must be a number from 1 to 24"); return false; } return true; } 

try{ if((int)item.value >= 1 && (int)item.value <=25){ //match. }else{ //error. } }catch (Exception e){ //type error } //or--- var itemValue = default(int); if(int.TryParse(item.value, out itemValue)){ if(itemValue >= 1 && itemValue <= 25){ //match. }else{ //error. } }else{ //item.value is not numeric. } 

You can add a private method and call it wherever necessary by passing textbox control which needs to be validated.

 private void ValidateText(TextBox textbox) { int value; bool isConverted = Int32.TryParse(textbox.Text.Trim(), out value); if (!isConverted) { MessageBox.Show("Only numbers allowed"); return; } if (value < 1 || value > 24) { MessageBox.Show("Please enter a value between 1-24"); } } 

Validating txtHour by invoking above method

ValidateText(txtHour); 

Look into doing your check with the OnKeyPress/OnKeyDown/OnKeyUp events:

http://msdn.microsoft.com/en-us/library/system.windows.forms.control.keypress.aspx

This is a very simplistic implementation but, this will achieve the validation that you are asking for:

int hoursEntered; bool isInteger; isInteger = int.TryParse(txtHour.Text, out hoursEntered); if (hoursEntered < 1 || hoursEntered > 24 && isInteger == true) MessageBox.Show("Your number is either less than 1, greater than 24 or you didn't enter a number", "Warning!", MessageBoxButtons.OK); 

There are a few things to consider here though. I wrote this code and had it tied to the event handler for a button click. If that is not your implementation, then I would strongly consider using the OnKeyPress/OnKeyUp/OneKeyDown events to do your validation. Otherwise, you can just copy this code into whichever button click event handler you already have in-place.