need a loop for update records

I have emp table with 3 columns:  emp_no, salary and remaining_salary.  I have a total 1000 to begin with.  Now, I like a loop to update (like update emp set remaining_salary = 1000- salary  ) to display the following the result data. When comes to 0 then exit.   How to do this in a for loop?  Thanks.

emp_no  salary   remaining_salary
1             300           700
2              400          300
3              500          0
4          600             0Start Free Trial