*    r_sq <= (x-h)_sq + (y-k)_sq <= R_sq
      **    annulus equation
       IDENTIFICATION DIVISION.
       PROGRAM-ID. EQUATIONTEST.
       DATA DIVISION.
       FILE SECTION.
       WORKING-STORAGE SECTION.

      *Equation Variables
       01  DIAMETER-RECEIVE-SMALL      PIC 9(4).
       01  DIAMETER-RECEIVE-LARGE      PIC 9(4).

       01  RADIUS-SQ-1                 PIC 9(4).
       01  RADIUS-SQ-2                 PIC 9(4).

       01  COORD-VARIABLES.
           03  X-COORD-SET                 PIC 9(4).
           03  Y-COORD-SET                 PIC 9(4).
           03  X-COORD-VAR                 PIC 9(4).
           03  Y-COORD-VAR                 PIC 9(4).


      *Arithmetic Variables
       01  ARITHMETIC-VARIABLES.
           03  X-VAR-MINUS-X-SET           PIC S9(4).
           03  X-VAR-MINUS-X-SET-SQ        PIC 9(4).
           03  Y-VAR-MINUS-Y-SET           PIC S9(4).
           03  Y-VAR-MINUS-Y-SET-SQ        PIC 9(4).

      *These are used to test if the equation is working.
       01  FINAL-VALUE                     PIC 9(4).

       01  BLACK-PIXEL                  CONSTANT 00.
       01  IMAGE-PIXEL                  CONSTANT 11.

       PROCEDURE DIVISION.
       MAIN-LOGIC.
           PERFORM RADIUS-INITIALIZATION.
           PERFORM COORD-INITIALIZATION.
           PERFORM RADIUS-CALCULATION.
           PERFORM COORD-CALCULATION.
           PERFORM COORD-CALCULATION-2.
           PERFORM CHECK-ROUTINE.
           STOP RUN.

       RADIUS-INITIALIZATION.

           DISPLAY "Please enter the diameter for the inner and outer"
           "circles of the annulus."
           DISPLAY "Inner Circle:".

           ACCEPT DIAMETER-RECEIVE-SMALL.
           DISPLAY "Outer Circle:".
           ACCEPT DIAMETER-RECEIVE-LARGE.
           DISPLAY DIAMETER-RECEIVE-SMALL " " DIAMETER-RECEIVE-LARGE.
           DISPLAY DIAMETER-RECEIVE-SMALL " " DIAMETER-RECEIVE-LARGE.


       COORD-INITIALIZATION.
      *In the final program this whole operation must be done with FILE.
           DISPLAY "Enter the central X and Y coordinates:".
           ACCEPT X-COORD-SET.
           ACCEPT Y-COORD-SET.

           DISPLAY "Enter the test X and Y variables:".
           ACCEPT X-COORD-VAR.
           ACCEPT Y-COORD-VAR.


       RADIUS-CALCULATION.
      * Calculate Radii Squares
           COMPUTE DIAMETER-RECEIVE-SMALL ROUNDED
                 = DIAMETER-RECEIVE-SMALL / 2.

           COMPUTE RADIUS-SQ-1
                 = DIAMETER-RECEIVE-SMALL * DIAMETER-RECEIVE-SMALL.

           COMPUTE DIAMETER-RECEIVE-LARGE ROUNDED
                 = DIAMETER-RECEIVE-LARGE / 2.

           COMPUTE RADIUS-SQ-2
                 = DIAMETER-RECEIVE-LARGE * DIAMETER-RECEIVE-LARGE.


       COORD-CALCULATION.
      * Calculate Distance Squares (using Signed variables)
           COMPUTE X-VAR-MINUS-X-SET = X-COORD-SET - X-COORD-VAR.

           COMPUTE X-VAR-MINUS-X-SET-SQ
               =   X-VAR-MINUS-X-SET * X-VAR-MINUS-X-SET.


           COMPUTE Y-VAR-MINUS-Y-SET = Y-COORD-SET - Y-COORD-VAR.

           COMPUTE Y-VAR-MINUS-Y-SET-SQ
               =   Y-VAR-MINUS-Y-SET * Y-VAR-MINUS-Y-SET.


       COORD-CALCULATION-2.
           COMPUTE FINAL-VALUE =
                        X-VAR-MINUS-X-SET-SQ
                           + Y-VAR-MINUS-Y-SET-SQ.


       CHECK-ROUTINE.
           IF RADIUS-SQ-1 <= FINAL-VALUE AND FINAL-VALUE <= RADIUS-SQ-2
               DISPLAY IMAGE-PIXEL
                   ELSE DISPLAY BLACK-PIXEL
                       END-IF.