I have problem , it repeats enterMarkC for every Student in the list, check for student numbber work...
Currently I am trying to set the attribute of Student class (courseworkMark) by user input.
Looking forward for help with it.
I would guess that what number equals after the statement "number = sc.next()" and what is returned by "if(s.getStudentNo().contains(number))" are not behaving the way you would like them to. Add some print statements to double check your input value and expected results. Also, I would add a break in your loop once you find the correct Student.
If this is for a class and you are allowed to go further I would definately use Devaka's suggestion to use a Map to make this much much easier. Each Student has a unique number... so you could skip the loop and find the correct Student in one statement using a Map.