C :: Add More Student Information To The Specific Txt File?

I'm trying to add more student information to the specific txt file. I did struct my student information and separated it with an array with max size of 200.

The inside of my current file looks like

Toshi
Aka
Nonal
Donald

The first one represent student[0] and next one is student[1] and so on till student[199]. Right now, only 4 space is occupied, which means the array has information till student[3] but not from student[4] (I guess it has null condition).

What I want to do is, I want to add a new student information to student[4] and till student[199] once at each time.

So, my prompt will look like
Would like to add a new student? Y/N
(if yes goes to below statement and exit if NO)
Hi. Please enter the information of new student. ___________
Student added. Please press any key to continue.

If the key is pressed, it goes back to my initial prompt and continues till I press N.

I sure I'm not using for loop to do this thing, because I'm adding student name one by one.

However, the array is already occupied by other student name till student[3] so, I want to add a new student information to student[4] (I don't want to overwrite the current information). And if student[4] is occupied, then [5] and so on.