Input string was not in a correct format.how to solve?

You probably mean the following (where price, totalprice and txtquantity are objects):

protected void totalprice()
    {
        int quantity = int.Parse(txtquantity.Text);
     float price =float.Parse(price);
     float totalprice = float.Parse(totalPrice);
     totalprice=quantity * price;
}

You need to learn the Type casting in C#. Have a look at these:

http://msdn.microsoft.com/en-us/library/ms173105.aspx[^]

http://msdn.microsoft.com/en-us/library/ms173105%28v=vs.80%29.aspx[^]

hope it helps :)

Using Int.TryParse or Float.TryParse is better than casting or converting the output values directly.

This error occurs when trying to convert a value which is not convertible to the desired datatype.

Regards,
Eduard

how can you convert string value "txtquantity" in to integer..?? and "price" into float, and "totalPrice" into float.

if these are text boxes then try this..

protected void totalprice()
    {
try{
        int quantity  = int.Parse(txtquantity.Text);
     float price =float.Parse(price.Text);
     float totalprice =   quantity * price;
}
catch(Exception e){ //output e to see}
    }

if these are string variables then, try this..

protected void totalprice()
    {
try
{
        int quantity  = int.Parse(txtquantity);
     float price =float.Parse(price);
     float totalprice = quantity * price;
} catch(Exception e) { //output e }
    }

I don't understand your problem.You are trying to Convert a String Value into Integer and trying to store it into Integer Variable which is not possible.If txtquantity is the TextBox then you have to save the TextBox value into the Variable befor Calculating Total Price.See this code.

int _quantity = int.Parse(txtQuantity.Text);
float _price = float.Parse(txtPrice.Text);
float _totalPrice = _quantity * _price;
txtTotalPrice.Text = _totalPrice;

This is the proper way to perform calculation.If you want somthing another output then please explain your question in brief.

-MKB

How do you want to convert string "txtquantity" to an integer value ?

Maybe you should use something like Request.Parameters["txtquantity"].ToString() or Session["txtquantity"].ToString() or txtquntity.Text .

So try to identify your source of values more carefully.