World of Ham Radio 1994 January

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Chapter 5 page 1 STARTREK THE COMPUTER PROGRAM By Joe Kasser CHAPTER 5 5.1 Using the Sub-systems Before any of the sub-systems can be used they must be in working order. Thus the state of each on-board sub-systems has to be stored and tested before any sub-system is used. This task is performed by the Damage Control subroutine. 5.2 Damage control The damage control section is an important part of the Starship. It keeps track of the state of repair of all the subsystems and allows the player to activate that system only if it is working order. Thus for example, the player cannot use Phasers to shoot at the enemy if the Phaser Banks have been damaged. The state of the subsystems are stored in an array labeled D(I) such that D(0) = the state of the Engines (Navigation) D(1) = the state of the Short Range Sensors D(2) = the state of the Long Range Sensors D(3) = the state of the Phasers D(4) = the state of the Photon Torpedoes D(5) = the state of the Computer D(6) = the state of the Shields etc. Gaining access to the state of any sub-system is then a matter of accessing the appropriate element in the array. For example, if the state of the Phaser Banks is required, looking at the contents of the fourth element of the array counting from 0 or D(3) will tell us how they are. A damage control status display shows the state of any damaged sub-system by displaying its name and the estimated time for repairs to be completed (ETR) as shown in the following typical display. DAMAGE CONTROL AT QUADRANT 4,6 SYSTEM ETR LONG RANGE SENSORS 1 PHASERS 2 HOW MANY DAYS TO SPEND ON REPAIRS SIR ? The state of the Long Range Sensors and the Phaser banks are shown together with their estimated time to complete repairs (ETR). The player is also asked to allocate time to perform the repairs. If the player chooses not to wait for the repairs to be performed, but move around and take the chance of fighting only armed with torpedoes, zero time can be entered as a response to the question. Copyright (c) Joe Kasser 1989 Chapter 5 page 2 STARTREK THE COMPUTER PROGRAM By Joe Kasser If the ETR is stored in the elements of the array directly, then examining the contents of any element will tell us how long it will take for the sub-system to be repaired. For example, if the value stored in D(4) is 2 then the ETR for the Phaser Banks is between 1 and 2 stardates. If the value stored in the element is 0 then that sub-system is in working order. Conversely any sub-system containing a value greater than 0 in the D(I) array, is damaged. Using this principle we can display the state of the sub-systems, fix any of them by setting the contents of the element to 0 or damage something by setting the contents of the particular element to a positive value. The flow chart for the damage control subroutine is shown in figure 5.1. The procedure begins by displaying the heading. A loop is then performed to identify if any sub-system is damaged (ie, check if the value stored in the D(I) matrix is greater than zero. If none of the sub-systems are damaged, a message is displayed accordingly. If at least one is damaged, the estimated time to repair stored in the array associated with the damaged sub-system is displayed. Repairs are in order only if the condition is not Red, namely, there are no Klingons in the Quadrant. If this condition is true, the repair time allocation is requested and the repairs carried out. If anything is fixed, that happening is displayed. Finally the time remaining in the game is adjusted to cover the time that has passed performing the repairs. The technique used to display the state of the contents of the D(I) array is to sample the contents of each element of the array in turn and test to see if it equal to 0. If it is greater than 0, damage is present. The BASIC statement to test something is the IF statement. The state of the contents of each element in turn can be tested by a set of statements such as IF D(I) = 0 THEN A set of such statements where I = 0, in the first one, I = 1 in the second one can be used as follows 2801 IF D(0) = 0 THEN 2821 2811 REM LINE SOMEHOW DISPLAYS THE DAMAGE MESSAGE 2821 IF D(1) = 0 THEN 2841 2831 REM LINE SOMEHOW DISPLAYS THE DAMAGE MESSAGE 2841 IF D(2) = 0 THEN 2861 2851 REM LINE SOMEHOW DISPLAYS THE DAMAGE MESSAGE and so on for all the elements in the array. This is a perfectly valid section of a program but there is a better way. We know that there are up to C1 elements in the array (0, 1, 2, 3, 4, 5, and so on). Change the routine to read 2801 LET I = 0 2811 IF D(I) = 0 THEN 2831 2821 REM SOMEHOW DISPLAY THE DAMAGE MESSAGE IN THIS LINE Copyright (c) Joe Kasser 1989 Chapter 5 page 3 STARTREK THE COMPUTER PROGRAM By Joe Kasser 2831 LET I = I + 1 2841 IF I < C1 THEN 2811 2851 REM PROGRAM FLOW CONTINUES HERE AFTER THE LOOP While this technique works, it puts the onus on the programmer to increment the loop counter (I) for each pass through the loop. BASIC contains a built in loop counter that takes care of the loop counter. Using the 'FOR/NEXT' pair of statements, the loop can be constructed as follows 2801 FOR I = 0 TO C1 : REM TEST C1 ELEMENTS 2811 IF D(I) = 0 THEN 2831 2821 REM SOMEHOW DISPLAY THE DAMAGE MESSAGE IN THIS LINE 2831 NEXT 2841 REM PROGRAM FLOW CONTINUES HERE AFTER THE LOOP The 'FOR/NEXT' construction thus may be used to simplifY the construction of loops. BASIC also builds into the 'FOR/NEXT' loop the capability to advance the loop counter by more than one step per pass using the 'STEP' statement. 2801 FOR I = 0 TO C1 STEP 2 will for example loop using values of I equal to 0, 2, 4 and 6 sequentially, and will skip values of I equal to 1, 3 and 5 So far the discussions have not considered how the state of the sub-system is displayed. The technique used here is to store the names of each sub-system in a String Array, D$(I) in the same order as the D(I) array that contains the state of the system. Lines 4570/4590 set up the names of each of the C1-C2 subsystems that can be damaged in an array containing C1 elements labeled D$(I) which happens to be a part of the array used to store the C1 command function names, such that D$(0) = "WARP ENGINES" D$(1) = "SHORT RANGE SENSORS" D$(2) = "LONG RANGE SENSORS" D$(3) = "PHASER BANKS" D$(4) = "PHOTON TORPEDO TUBES" D$(5) = "MAP (COMPUTER)" D$(6) = "SHIELDS" ETC. Now the BASIC statement to display something at the terminal is PRINT. Thus PRINT D$(I) would print the name stored in the D$(I) array for the corresponding value of I. For example if you wanted all the names to be listed, you could type the following routine into the existing game program in the computer. Copyright (c) Joe Kasser 1989 Chapter 5 page 4 STARTREK THE COMPUTER PROGRAM By Joe Kasser 2811 REM DEMO LOOP 2821 FOR I = 0 TO C1 2831 PRINT D$(I) 2841 NEXT 2851 RETURN If you now type in the word RUN you tell the computer to execute your program. When you get the 'COMMAND ?' prompt, enter the word 'DAM' to initiate the Damage Control command. The resultant listing would be as follows WARP ENGINES SHORT RANGE SENSORS LONG RANGE SENSORS PHASERS PHOTON TORPEDOES COMPUTER SHIELDS LONG RANGE PROBES TRANSPORTER SHUTTLECRAFT DAMAGE CONTROL VISUAL RESIGN SAVE THE STATE OF THE GAME LOAD A SAVED GAME COMMAND ? At this time hold down the 'CNTRL' (Control) key with one finger and touch the 'C' key with the other. You have just interrupted the program in mid-flow by typing in the Control-C character also written as ^C. The computer should give you message saying that a BREAK occurred. In our instance we want to print out the name of the sub- system and its estimated repair time, namely two things. BASIC allows that by the use of the comma (,) or semi-colon (;) separators. For example the statements 2831 PRINT D$(I),D(I) and 2831 PRINT D$(I);D(I) do not perform the same operation. The semi-colon displays the second (or subsequent) item to be displayed immediately following the previous one, while the comma performs a tab function which moves the printhead or cursor over to the next tab position just as an electric typewriter. So from before, the FOR/NEXT routine to display the names of the sub-systems and their repair times would thus require changing line 2831 to Copyright (c) Joe Kasser 1989 Chapter 5 page 5 STARTREK THE COMPUTER PROGRAM By Joe Kasser 2831 PRINT D$(I),D(I) Again type RUN (carriage return). When you get the 'COMMAND ?' prompt, try the 'DAM' command. The resultant listing will not be perfectly formatted. Try it and see. The reason that the display is not formatted properly is because the lengths of the names of the sub-systems are different. The built in tab feature in BASIC will only tab across to the next tab position. You can set your own tab position anywhere along the line by using the TAB statement. If line 2831 is changed to 2831 PRINT D$(I) ; TAB(28) ; D(I) the result will be formatted correctly. Break the program (^C), change line 2831 and try it. The flow chart for the DAMAGE.CONTROL function may be implemented in BASIC as shown in figure 5.2. Consider each of the lines in turn, what they do and how they do it. The damage control function begins at line 2800 with a REMark or comment statement telling you what function is being performed. It has already been mentioned that the most commonly used subroutines are placed towards the beginning of the program. This is done to speed up execution time, since most BASIC interpreters search for line numbers sequentially from the top. When you enter a line of code into a program in the interpretive mode, the interpreter finds the position for the line and inserts it in the correct place in the sequence of statements. The Damage Control subroutine begins with the REMark statement in line 2800. Line 2810 uses the subroutine at line 70 to display the name of the function being performed. A temporary variable, D8 is then set to 0. A loop in lines 2820 and 2830 tests the status of each of the subsystems that can be damaged in the damage control or commands array D(I). There are C1 commands but only C1-C2 of them can be damaged. Damage control cannot be damaged, that doesn't make sense. Visual sensors similarly can't be damaged, and you can always try to resign. The use of C1-C2 in line 2820 and later lines, allows the routine to work if further commands are added. Adding a new command later should only require changes in the command subroutine, it should not require changes anywhere else in the program. When you write programs keep them modular and make the modules stand-alone. That means that changes in one function should not require changes in more than one module. If you write code that requires modifications to many of its modules when implementing a change you will spend an awful lot of time performing de-bugging, because you will have to do a lot of searching to find where the modifications have to be made. Copyright (c) Joe Kasser 1989 Chapter 5 page 6 STARTREK THE COMPUTER PROGRAM By Joe Kasser If the value assigned to any sub-system in the array is greater than zero, ie. signifying that something is damaged the value of D8 is incremented by one. At this time, we are not looking to see what is damaged, just if something is. A PRINT statement is then executed to cause the display to advance one line at the console and the value of D8 is tested. If it is equal to zero then nothing is damaged and a message is displayed accordingly. There is then no need to continue in the subroutine and the GOTO 2910 statement causes the program to branch forward to line 2910 skipping the remainder of the subroutine. The exact value of D8 is not important at this time. It is however at this time, a count of how many of the sub-systems are damaged. The damage control display begins at line 2840. This line displays the heading. The loop in lines 2850 and line 2860 now examine the state of each item in the array. If any are damaged, that fact is detected in line 2850 and a display of the name of the sub-system and its estimated time to repair is made. The estimate is printed out as an approximate number as follows. The statement used is PRINT INT(D(I)+Z). This takes the value stored in the array, adds 1 to it and then converts the result to an integer. this process is known as in mathematics as "rounding up" to the next significant digit. The process could have been written as X = D(I) + Z : X = INT(X) : PRINT X which would do the same job but require the use of an extra (dummy) variable 'X'. The display is formatted by the TAB(28) statement. After the state of all the systems have been sampled, the presence of Klingons in the quadrant is then determined. If the value of the variable K is greater than 0, at least one Klingon is present in the quadrant (we don't care how many at this time) and the subroutine ends at this time by GOing TO line 2910. At this stage we have reached line 2870. There are no klingons in the quadrant so the value assigned to K is zero. A 'PRINT' statement is executed and the computer then requests the number of stardates to be spent on repairs, using the 'INPUT' statement and the prompt "HOW MANY DAYS TO SPEND ON REPAIRS SIR ". Note the space after the SIR. This space separates the SIR from the ? that BASIC displays to inform the user that an input is being requested. The player's reply is assigned to the variable D8. D8 is thus re-used at this time. Re-using variables is good practice because it saves memory, but on the other hand, can lead to problems if the state of variables are changed by different routines because it may be difficult to find out where the change is being made. The player's input is first checked to see if a negative number was Copyright (c) Joe Kasser 1989 Chapter 5 page 7 STARTREK THE COMPUTER PROGRAM By Joe Kasser input. If it was, the value of D8 is set to zero. After all we cannot allow negative time in the game. The repairs are performed in lines 2880 to 2900. For each sub-system liable to damage a test is performed. If the sub-system is undamaged, nothing happens to it and the program skips to line 2900. If however it is damaged (the value assigned to D(I) > 0 ) then line 2890 is performed. The value assigned to D8 is subtracted from the number stored in the array. If the result is equal to or less than zero repairs have been completed and the sub-system should be in working order. The value in the damage control status array is then set to zero and a message that the sub- system has been repaired is displayed at the console. When all is said and done, line 2910 causes the subroutine to RETURN to the main program loop. The DAM subroutine uses one nested subroutine starting at line 70 to format the headings on the various commanded displays. Line 70 contains the comment while the operation is performed by line 80. The name of the operation stored in the D$(I) array is first displayed, followed by the words 'AT QUADRANT'. The computer counts the quadrants from 0 to 7, but the player counts them from 1 to 8. The adjustment is performed by the Q1+Z and Q2+Z statements. Take careful note of the formatting semi colons used in the line. When this subroutine is called, the value of I has been set up in the command matching loop of lines 3060/3070 for the branch using the 'ON' statement in line 3080. At first glance it seems that this procedure is too complex. why not just subtract the D8 from D(I) for each element in the array, and display a message for those having a result less than zero. Well why not? the answer is a question. How do you then detect the difference between systems in working order and those that have just been repaired? Delete lines 2811 to 2851 by typing 'DELETE 2811-2851' into the computer. Notice the use of the 'DELETE' statement which can be used to delete all or selected parts of a program. Here we just deleted the temporary lines we used to play with the formatting of the Damage Control Status display. The format of the command is the same as that of the 'LIST' command. Some dialects of BASIC may require a slightly different way of typing the command (e.g. DELETE 2811,2851). Add lines 70, 80 and line 2800 to 2910 (as listed in figure 5.2) to the program and save the program. Then RUN it. The damage control command should work as should the "Help" command (Command 0). Interrupt the program flow with a ^C and dummy in some damage. You do that as follows. Let us enter some damage to the one sub-system by typing in D(3) = 4 which sets the damage status of device 3 to 4 stardates estimated repair time. What we have done is interactively entered some data directly into a variable from the console. It is a good way to debug the program. Now to continue the program just type in Copyright (c) Joe Kasser 1989 Chapter 5 page 8 STARTREK THE COMPUTER PROGRAM By Joe Kasser CONT. Do not type RUN or the computer will reset all variables to zero and you will lose your input for D(3). If you now execute the Damage Control command you will get a notice that one sub-system is damaged. Enter a repair time allocation of 2 stardates, and try the command again. See how the ETR has changed. Now enter a repair time of 5 days and see if you get a "REPAIRED" message. You should. You have now exercised the damage control function and are ready to go onto bigger and better things. The next command to activate is the MAP (COMPUTER) command so that we can take a look at how the galaxy was set up. 5.3 The Map Display The map display is one of the Ship's computer functions. It is directly accessible from the main command loop as well as from the computer. It shows the contents of all the quadrants in the galaxy that have been scanned by Long Range or Short Range sensors or by Long Range Probes as a three digit number with the following convention. The 100's digit = number of Klingons the 10's digit = number of Starbases the 1's digit = number of Stars, thus for example, 317 means that the quadrant contains 3 Klingons, 1 Starbase and 7 stars. Quadrants that are unscanned show up as "***" on the display. The flow chart to implement the MAP function is shown in figure 5.3. The nested loops can be seen at a glance. The same nesting technique is used as in the initialization routine. The routine first tests to see if the map function is damaged. If it is, a message is displayed stating that fact, if not, it is assumed to be in working order and a map display is generated. The map displays the contents of each of the quadrants and emphasizes the quadrant containing the Enterprise. In this version of the game, that emphasis is to display the quadrant containing the Enterprise surrounded by '+' signs. A sample map display is shown below. Copyright (c) Joe Kasser 1989 Chapter 5 page 9 STARTREK THE COMPUTER PROGRAM By Joe Kasser MAP FOR QUADRANT 4,6 1 2 3 4 5 6 7 8 1 *** *** *** *** *** *** *** *** 2 *** *** *** *** *** *** *** *** 3 *** *** *** *** *** *** *** *** 4 *** *** *** 001 012 104 *** *** 5 *** *** *** 002 +206+ 307 *** *** 6 *** *** *** 717 001 003 *** *** 7 *** *** *** *** *** *** *** *** 8 *** *** *** *** *** *** *** *** The map display function can be written in BASIC as shown in figure 5.4. The sequence begins at line 200 with the usual REMark statement. Then line 210 tests the state of repair of the MAP/COMPUTER. If it is in working order namely if D(I) = 0 then the program flows on to line 220 skipping over the rest of line 210 which displays a message stating that the device is damaged and causes the subroutine to exit via line 280. Line 210 could alternatively be written using the IF/ELSE construct as 210 I=5 : IF D(I)=0 THEN 220 ELSE PRINT D$(I); "DOWN AT THIS TIME" : GOTO 280 this version of line 210 needs a dialect of BASIC that not only recognizes the IF/ELSE construct, but also branches to the next subsequent line number if the test fails. Which version is used basically depends on the programmer. They all perform the same operation. The implementation of the IF/ELSE-THEN statement in BASIC may differ from version to version and tends to cause the most problems when converting programs. 5.4 LONG RANGE SENSORS Long Range sensors show the contents of the neighboring quadrants but in minimal detail. An example of a long range sensor scan is shown below; LONG RANGE SENSORS FOR QUADRANT 4,6 001 012 104 002 206 317 717 001 003 The Enterprise is located in the quadrant shown in the center of the display. The contents of each quadrant are described as a three digit number with the following convention. The 100's digit = number of Klingons the 10's digit = number of Starbases the 1's digit = number of Stars, thus for example, 317 means that the quadrant contains 3 Klingons, 1 Starbase and 7 stars. Quadrants that are outside the galaxy show up as "***" on the display. Copyright (c) Joe Kasser 1989 Chapter 5 page 10 STARTREK THE COMPUTER PROGRAM By Joe Kasser The display shows a small section of space around the quadrant that the Enterprise is located in, in a similar format to that of the Map display. This means that the display is relative to the position of the Enterprise. The Enterprise is always located in the center quadrant. The flow chart for the procedure is shown in figure 5.5. The routine begins with a test to see if the sensors are damaged. If they are a message to that effect is displayed at the console and the subroutine skips everything else. If they are not, the standard sensor subsystem heading is displayed and the loops to perform the actual display functions begun. The loop counters each contain three iterations of their respective loops. This sensor display shows the contents of space with the co-ordinates of the Enterprise as the center. The row display is thus with respect to Q1, the column display with respect to Q2. The inside loop scans the quadrants in adjacent columns to the Enterprise, the outside loop adjusts the row counter so that the operation is performed on adjacent rows as well. The quadrant containing the Enterprise is also scanned. Thus for each quadrant in the loop, a test is first performed to determine if the quadrant is inside the galaxy. If the quadrant is inside the galaxy, and if the computer/map is not damaged, the map array is updated. The contents of the quadrant are then displayed at the console irrespective of the state of the computer. As long as the Long Range Sensors are working, the player will always get a scan display. The map however will only be updated, if the ship's computer is also up. If the quadrant being scanned is outside the galaxy, the display will be "***". The cursor is moved over one character by displaying a "space" character, and the loop continues with the next quadrant in the row. When the row has been scanned by the inner loop, the outer loop advances its loop counter to perform the operation on the next row. Since the next row is to be displayed on the next line the cursor is advanced to the start of the next line before the next set of quadrants are displayed. When the contents of all nine quadrants have been displayed, the subroutine terminates. The BASIC language implementation of the flow chart is shown in figure 5.6. The routine starts at line 300 with a REMark or comment. Line 310 checks to see if the sensors are working (ie. if D(I) > 0 ). If they are working, the 'IF' test fails and the program continues on line 320. If they are damaged, the program continues along line 310, displaying a "DAMAGED" message and then branching forward to the RETURN statement in line 370. You will see many instances in many published programs where line 310 or its equivalent will contain a 'RETURN' statement instead of the 'GOTO the line which terminates the subroutine'. Both execute correctly, however it good practice to ensure that any subroutine has only one exit point. It will make debugging a lot Copyright (c) Joe Kasser 1989 Chapter 5 page 11 STARTREK THE COMPUTER PROGRAM By Joe Kasser simpler. Line 320 uses the subroutine beginning at line 70 to display the heading for the sensor scan display, and then proceeds to set up the loops for the row and column displays. The Long Range Sensor display uses the same format as the Map display. The map displayed the whole galaxy, but here in the Long Range Sensors we only want to see what is in the adjacent quadrants. Namely we want to look at quadrants on each side of the Enterprise's location. Since the Enterprise is located at quadrant Q1,Q2 at any time, our loop range must be the co-ordinates of the Enterprise plus or minus one. Thus the program statement FOR I = Q1 - Z TO Q1 + Z : FOR J = Q2 - Z TO Q2 + Z. The PRINT " "; part of line 320 advances the cursor between quadrant displays on the same line. Line 330 tests to see if the quadrant being scanned is outside the galaxy. Quadrants within the galaxy are numbered from 0 to 7. Thus any quadrant with a row or a column number of less than 0 ( <0 ) or greater than 7 ( >7 ) is out of the galaxy by definition. The display for those quadrants is always a "***". The program flow then jumps forward to NEXT statement in line 360. If the quadrant being scanned is inside the galaxy, line 340 tests the state of repair of the map/computer. If it is up, the quadrant scanned is entered into the computer. The quadrant is scanned using the ABS(X) function. This function converts a number to its absolute or positive value. Thus a positive value remains a positive value, while a negative value is changed to a positive one. We thus don't care what the previous state of the quadrant was before being scanned. Lines 350, 360 and 370 perform the same functions as line most of line 250, lines 260, 270 and 280 respectively. If you want to save memory space you could delete lines 350 to 370 and replace them by 350 GOTO 270 If you do this, you will also have to change the references to those line numbers in lines 310 and 330. For example in line 330 you will have to change the 360 to 250. Since comprehension of the program is easier if lines 350 to 370 are used, the program has been written using them. Feel free to make the change if you want to. You will also change the format of the display slightly. Try it later on, and keep the version you like better Carefully copy line 300 to 370 into your program. Debug them as follows. First RUN the program. Perform the MAP command. You should get the same unscanned display as before. If the whole map shows up scanned, you forgot to delete line 211. In that case, break the program and do it now. ReRUN the program. Now do a Long Range Sensor command (LRS). You should then see the normal long range sensor display. Then repeat the map command, and the quadrants that were scanned by the long range sensors should show up scanned on the map. It is then time to break the program (^C). Damage the Copyright (c) Joe Kasser 1989 Chapter 5 page 12 STARTREK THE COMPUTER PROGRAM By Joe Kasser computer which will in effect damage the map by entering D(5) = 3. CONTinue the program and try the 'MAP' command. It won't work. Try the 'LRS' or Long Range Sensor command. Now use the 'DAM' or Damage Control command to fix the map and request another display. The map should still be completely unscanned, because the computer (map) itself was damaged at the time that the long range scan was performed. Break the program again and damage the long range sensors by entering D(2) = 1. CONTinue it and try the long range sensors again. They won't work. Fix them and try the sensors followed by the map again. The sensors should work, and the map display should also update. If you like, break the program again and change the position of the Enterprise by changing the values of Q1 and Q2. when you continue the program, the long range scan will illuminate and update a new section of the galaxy (if your new values for Q1 and Q2 were within the range of 0 and 7 inclusive). If you made any changes to the program during the debugging session,save the program again at this point. 5.5 Long Range Probes Long Range Probes are a means to find out what lies beyond the range of the Long Range Sensors without moving. You can fire a probe in any direction just as you would fire a photon torpedo. The probe speeds away at about Warp Factor 10, as such it takes about 0.1 stardates to cross a quadrant. The probe sends back a status report in the same format as the long range sensor/map data, as it enters each new quadrant. The data received from the probe is automatically placed into the computer, if the computer is up at the time that the data is received. The communications technology used by the probes give it a limited range however. The signal grows too weak to be received when the probe is about five quadrants away from the Enterprise. If the probe enters a quadrant containing Klingons there is a probability that they may detect and destroy it. Should you try and launch one when in a battle situation, the simulator will stop you. 4300 REM LONG RANGE PROBE (LRP.ASC) 4310 IF D(I)>0 THEN PRINT "LAUNCH CONTROL INOPERATIVE AT THIS TIME" : GOTO 4470 4320 L3=L3+Z : IF L3>7 THEN PRINT " No Probes left... Sir " : GOTO 4470 4330 IF K>0 THEN PRINT "You are not allowed to launch a probe during a battle" : GOTO 4470 4340 PRINT "LRP";L3;"Direction (1-9) "; : INPUT C : IF C=0 THEN 4470 4350 IF C<Z OR C>9 THEN 4340 4360 X1=Q1 : Y1=Q2 : X2=Q1+.5 : Y2=Q2+.5 : T1=T : FOR I=0 TO E0 : T=T-.1 4370 Y=(C-Z)*.785398 : X=COS(Y) : Y=-SIN(Y) 4380 X2=X2+Y : Y2=Y2+X : X1=INT(X2) : Y1=INT(Y2) 4390 IF SQR((X1-Q1)^2+(Y1-Q2)^2)>5 THEN PRINT "Probe out of range" : GOTO 4460 4400 PRINT X1+Z;",";Y1+Z;" ="; 4410 IF X1<0 OR X1>7 OR Y1<0 OR Y1>7 THEN PRINT "***" : GOTO 4450 Copyright (c) Joe Kasser 1989 Chapter 5 page 13 STARTREK THE COMPUTER PROGRAM By Joe Kasser 4420 E$=STR$(Q(X1,Y1)) : E$="00"+MID$(E$,2) : PRINT RIGHT$(E$,3) 4430 IF D(5)=0 THEN Q(X1,Y1)=ABS(Q(X1,Y1)) 4440 IF RND(Z)<ABS(Q(X1,Y1)+Z)/1000 THEN PRINT "Contact lost with probe" : GOTO 4460 4450 NEXT 4460 GOSUB 1800 4470 RETURN 1800 REM SUBROUTINE FOR REPAIRS AFTER TIME (T1-T) 1810 IF T<0 THEN F9=4 : GOTO 1870 1820 N=0 :FOR I=0 TO C1-C2 : IF D(I)=<0 THEN 1860 1830 D(I)=D(I)-(T1-T) : IF D(I)>0 THEN 1860 1840 IF N=0 THEN PRINT : PRINT "DAMAGE CONTROL REPORTING " : N=Z 1850 D(I)=0 : PRINT D$(I);"REPAIRED" 1860 NEXT 1870 RETURN An alternative approach to implementing Long Range Sensors is to send them on their way and allow time to pass while they report back. If we assume that probes travel one quadrant per stardate we can set up a scenario in which the program that implements the function is split into two sections, namely one to launch the probes, and the other that deals with the reporting. This can be somewhat (but not absolutely true) considered as foreground - background programming, in which the probes are launched in foreground, where the action is, while the reporting is done in background as time goes by. The flowchart and code for the launching function would be as shown below. : PROBELAUNCH PROBES.DAMAGED =? YES (1) DISPLAY.MESSAGE NO (1) PROBE.AVAILABLE =? YES (2) REQUEST.AND.ACCEPT.COURSE LAUNCH.PROBE KLINGONS.IN.QUADRANT =? YES (3) DO.THEY.DETECT.PROBE =? YES (4) PROBE.DESTROYED THEN (4) THEN (3) NO (2) DISPLAY."NONE.LEFT".MESSAGE THEN (2) THEN (1) ; 8005 REM LONG RANGE PROBE LAUNCH 8015 IF D(I)>0 THEN PRINT "LAUNCH CONTROL INOPERATIVE AT THIS TIME : GOTO 490 8025 FOR I = 0 TO 7 : IF L3(I)>0 THEN 8075 8035 INPUT "Course (1-8.99)";L4(I) : IF L4(I) = 0 THEN 8085 8045 IF L4(I)<Z OR L4(I)>8.99999 THEN 8035 8055 IF K>0 AND RND(Z)<K/7 THEN PRINT "Probe destroyed by the enemy" : L3(I) = 2 : GOTO 8085 8065 L1(I)=Q1 : L2(I)=Q2 : L6(I) = Q1+.5 : L7(I)=Q2+.5 : L3(I)=Z : L5(I)=T : PRINT "Probe";I+Z;"launched Sir" : GOTO 8085 8075 NEXT : PRINT " No Probes left... Sir " 8085 RETURN 8095 REM Copyright (c) Joe Kasser 1989 Chapter 5 page 14 STARTREK THE COMPUTER PROGRAM By Joe Kasser Copyright (c) Joe Kasser 1989 Chapter 5 page 15 STARTREK THE COMPUTER PROGRAM By Joe Kasser The flowchart and code for the reporting function would be as shown below. : PROBE.REPORTING LOOP (max.number.of.probes) + PROBE.ACTIVE =? + YES (1) DAY.PASSED.SINCE.LAST.REPORT =? + PROBE.IN.RANGE =? 8105 REM LONG RANGE PROBE REPORTING 8115 FOR I = 0 TO 7 8125 IF L3(I) <> Z OR (L5(I) - T) < Z THEN 8235 8135 Y = (L4(I)-Z)*.785398 : X = COS(Y) : Y = -SIN(Y) 8145 L6(I) = L6(I) + Y : L7(I) = L7(I) + X : L1(I) = INT(L6(I)) : L2(I) = INT(L7(I)) 8155 IF SQR((L1(I)-Q1)^2+(L2(I)-Q2)^2)>5 THEN 8225 8165 IF L8 = Z THEN 8205 8175 PRINT "LRP";I+Z;"reporting from Quadrant";L1(I)+Z;",";L2(I)+Z;" ="; 8185 IF L1(I)<0 OR L1(I)>7 OR L2(I)<0 OR L2(I)>7 THEN PRINT "***" : GOTO 8225 8195 E$ = STR$(Q(L1(I),L2(I))) : E$ = "00"+MID$(E$,2) : PRINT RIGHT$(E$,3) 8205 IF D(5) = 0 THEN Q(L1(I),L2(I)) = ABS(Q(L1(I),L2(I))) 8215 IF RND(Z)<ABS(Q(L1(I),L2(I))+Z)/1000 THEN L3(I)=2 : IF L8=0 THEN PRINT "Contact lost with probe" 8225 L5(I) = L5(I) - Z : IF L5(I)>T THEN 8125 8235 NEXT : RETURN 8305 REM LONG RANGE PROBE STATUS 8315 GOSUB 70 : PRINT "PROBE";" QUADRANT";" SENSORS" 8325 FOR I = 0 TO 7 : PRINT I+Z;" "; : IF L3(I) = 0 THEN PRINT "READY FOR LAUNCH " : GOTO 8405 8335 IF L3(I) = 2 THEN PRINT "DESTROYED" : GOTO 8405 8345 IF SQR((L1(I)-Q1)^2+(L2(I)-Q2)^2)>5 THEN PRINT "OUT OF RANGE" : GOTO 8405 8355 PRINT L1(I)+Z;",";L2(I)+Z;" ";" "; 8365 IF L1(I)<0 OR L1(I)>7 OR L2(I)<0 OR L2(I)>7 THEN PRINT "$$$"; : GOTO 8395 8375 E$ = STR$(Q(L1(I),L2(I))) : E$ = "00"+MID$(E$,2) : PRINT RIGHT$(E$,3) ; 8385 IF D(5) = 0 THEN Q(L1(I),L2(I)) = ABS(Q(L1(I),L2(I))) 8395 PRINT 8405 NEXT : RETURN Copyright (c) Joe Kasser 1989