is there any widgets or something by using which i can immediately calculate the marks

the marks which can be seen after the user immediately after the exam or i  have to calculate the marks manually ?

I'm not sure if understood your question, this is our Form Calculation widget: http://widgets.jotform.com/widget/calculation. 

Take a look on this link to get more details about this widget: http://www.jotform.com/help/259-How-to-perform-calculation-in-the-form. 

If it does not help, please provide us the link/name of your form as well as more details, we will be glad to help.