Calculate Sum ( Add ) TextBox Values in ASP.Net and display result

hi,sir 

how to calculate a sum which get the data from a set of textboxes in asp.net page? can write in code behind c#?

Can assign the textbox value to a variable then calculate the sum at code behind them show the answer to the asp.net page? or is it have to write javascript to perform those action? how to do this? Waiting for your reply. Thank you