c++ sentinel loop

[weezy08]

So I'm making a file that calculates the total score for an individual student. the end of my linefeed will be -1. the first line determines the possible points and the rest of the lines are data for a particular student. There isn't a limit on how many student data the program can read. so i figured out the first line feed I'm just stuck on how the program will read each student data until it reaches the last one. and where do i calculate the percentage, whenever i check it, it always comes out as 0. Any help will be great! thanks!

Part of program.

cin >> number;

while (number != -1)
{
ctotal = ctotal + number;
cin >> number;
}


cin >> c1 >> c2 >> c3 >> c4;
cin >> data;
while (data != -1)
{
stotal = stotal + data;
cin >> data;
}

per = (stotal / ctotal) * 100;

[JLBorges]

int total = 0 ;
int score ;
while( std::cin >> score && score != -1 ) total += score ;

[dangerous]

ctotal should be initialized.