c# - Textbox entry giving errors -

i have 4 text boxes.
in first textbox doubleclicking , opening child form.
there displaying names , values.
selecting 1 name in form , name coming first form first text box , next text box value coming.
next want take input using third text box , caliculations, display result in fourth textbox(readonly one).
giving error.
made mistake.

//take values child form: private void datagridview1_celldoubleclick(object sender, datagridviewcelleventargs e) {        form8.code = datagridview1.currentrow.cells[0].value.tostring();        form8.name = datagridview1.currentrow.cells[1].value.tostring();     form8.fiel= datagridview1.currentrow.cells[6].value.tostring();     form8.measure= datagridview1.currentrow.cells[2].value.tostring();      //my main form store values:     boxname.text = name;     if (boxname.text == "")     {         messagebox.show("empty name");     }     else     {         boxbprice.text = fiel;         double qty = convert.todouble(boxqty.text);//taking quanty input     } 

where did mistake. giving error

"input string not in currect format"

"input string not in currect format"

the error means string you're trying parse doesn't contain double value.

• ensure field holds input data valid text representation of double value (in correct format).
• you use double.tryparse prevent error, you'd need debug program , see actual value of convert.todouble(boxqty.text); @ run time.

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example of using tryparse:

double number; if (double.tryparse(boxqty.text, out number)){   // value of number }