World of Ham Radio 1994 January

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Chapter6 PAGE 1 STARTREK THE COMPUTER PROGRAM CHAPTER 6 6.1 Short Range Sensors The Short Range Sensors are the means by which a short range radar scan is performed. They let the player examine everything that is in the Quadrant as well providing game status information. There are 64 sectors in the quadrant which is also organized as 8 rows of 8 sectors. In order for the computer to access each sector some technique must be employed to store the quadrant and the contents of the sectors into the computer. We have already discussed that the contents of the quadrant are stored in an array variable Q(I,J) as an array of rows and columns where I represents the row and J the column. The Quadrant array can thus be considered as having two dimensions and the contents of any quadrant can be defined using Q(I,J) where I and J define the row and column co-ordinates respectively (ie. Q(2,6) refers to the contents of a quadrant that is two rows down from the top corner and 6 columns along the row). Each quadrant itself contains 64 sectors, also arranged as an 8 by 8 array. The ground rules of the game only allow one object to be in a sector at any one time. The contents of the sectors are kept track of in an array similar to the quadrant array Q, but this time called S(I,J). For example, S(2,6) refers to the actual sector, the contents of the location in the array define what is in the sector. The contents can be set by using the LET statement such as LET S(2,6) = 1. The contents of any sector can be assigned a number corresponding to the occupant as follows, 1 represents a blank or empty sector 2 represents a star 3 represents the Enterprise 4 represents a Klingon (an enemy vessel) 5 represents a starbase An example of a Short Range Sensor scan is shown below. SHORT RANGE SENSORS IN QUADRANT 4,6 1 2 3 4 5 6 7 8 SCORE 511.3 1 . . . . . . . . TIME LEFT 23.9 2 * . . . . . . . CONDITION RED 3 . . . K . . . K SHIELDS 255.6 4 . . . . . . . . ENERGY 3456.0 5 . . . . * . . . PHOTON TORPEDOES 3 6 . . . * * . * . STARBASES 2 7 . . . . . E . . KLINGONS LEFT 21 8 . . . . . * . . KLINGONS CAPTURED 0 Copyright (c) Joe Kasser 1989 Chapter6 PAGE 2 STARTREK THE COMPUTER PROGRAM The occupants of the sector in the basic game can be any one of the following, . represents a blank or empty sector * represents a star E represents the Enterprise K represents a Klingon (an enemy vessel) B represents a starbase The game status information alongside the radar display is as follows; TIME LEFT The amount of play time left in the game. CONDITION The state of the Enterprise. There are three possible conditions, RED Battle area, enemy in quadrant YELLOW One of the sub-systems aboard the Enterprise is damaged, or the Energy level has fallen to below 400 units. GREEN Everything is fine, no enemy detected, no damage, and sufficient available energy aboard the ship. SHIELDS The amount of energy allocated to the ship's shields. If this energy level is ever beaten down to zero by the enemy, the Enterprise is destroyed and you lose the game. ENERGY The amount of energy on board the Enterprise. If this ever falls to zero, the Enterprise becomes a derelict in space, and you lose the game. PHOTON TORPEDOES The number of photon torpedoes remaining on board the Enterprise. STARBASES The number of starbase in the galaxy, even if you have not located them all. KLINGONS LEFT The number of enemy ships in the galaxy. Should you destroy them all, you will win the game. KLINGONS CAPTURED The number of enemy vessels you have captured. Each one captured is a bonus multiplier on your score. The flow chart for the Short Range Sensor routine is shown in figure 6.1. In order to perform a short range sensor scan, we first have to test if the short range scanners are damaged. If they are damaged, the contents of the quadrant cannot be scanned let alone Copyright (c) Joe Kasser 1989 Chapter6 PAGE 3 STARTREK THE COMPUTER PROGRAM displayed. Thus a message that tells the player that the sensors are broken is displayed. Assuming workable sensors, a test is performed to determine if the Enterprise is inside the galaxy. If it is inside the galaxy, and if the computer is up, the quadrant data is loaded into the Map. If the computer is down, the scan will take place, the information will be displayed on the screen, but the data will not be put into the map. The display heading is generated and the column numbers and score displayed. The display routine comprises a similar pair of loops to the map routine. Here the contents of the sector are shown as a letter, followed by a "space" character. At the end of each row, one item of game status information is displayed. The cursor is then moved to the start of the next line, and the loops continue. The BASIC language implementation of the flowchart can take the form shown in figure 6.2. Line 400 contains the REMark or comment. Line 410 tests the state of the sensors. If they are damaged, ie IF D(I) > 0 then a message that the sensors are damaged is displayed and the subroutine exits at this time, as since the sensors are damaged, there is no point is continuing in the sequence. Line 420 checks to see if the quadrant is outside the galaxy. If it is, the program flow advances to line 440 skipping the scanning of the quadrant. If this test was not present, BASIC would output an error message when it tries to update the Q(I,J) array for quadrants outside the galaxy. The reason for the error messages is that when Q1 or Q2 have negative values, the statement Q(Q1,Q2) is invalid. There is also no space allocated in the array for when Q1 and Q2 have values greater than 7. to store any data. The test used the OR statement to determine if any one of four conditions is met. If anyone of them is, the Enterprise is outside the Galaxy, because in order to be in the galaxy, the Q1 and Q2 co-ordinates of the ship must have values in the range of 0 to 7. The state of the ship's computer (D(5)) is tested in line 430. If it is working, ie. IF D(5) = 0 then the Map can be updated. The map is updated by the statement Q(Q1,Q2) = ADS(Q(Q1,Q2)) which makes the contents of the quadrant a positive number. This is the normal scanning technique as used previously. If the computer was damaged, the contents of the quadrant are not entered into the map, but the radar display is still performed beginning at line 440. Line 440 first uses the subroutine starting at line 70 to display the heading. It then determines the current condition of the Enterprise by calling the subroutine beginning at line 3400. It next displays the column number using the statement PRINT " 1 2 3 4 5 6 7 8"; which is a simple method of doing the job. The Long Range Sensor Copyright (c) Joe Kasser 1989 Chapter6 PAGE 4 STARTREK THE COMPUTER PROGRAM display used a different technique which was more complex. Two different techniques for doing almost the same job have thus been presented for your review. Which one is correct? They are both correct. In your future programs use the one you like best. The line is then tabbed across to the 20th character position by the TAB(20) ; and the subroutine starting at line 170 is invoked to display the current score. The line then sets up the row loop. Line 450 contains the column loop. It first displays the contents of each sector along the row and then tabs the cursor to the 20th character position along the display line. Before we look at line 450, consider for a minute how the contents of the sectors are distinguished. The contents of each sector S(I,J), can be set up to be an integer between 1 and 5 where 1 represents a blank or empty sector 2 represents a star 3 represents the Enterprise 4 represents a Klingon (an enemy vessel) 5 represents a starbase. So if for example, for any sector with co-ordinates (I,J), if S(I,J) = 4, there is a Klingon in that sector. Each of the objects that can be in a sector are represented by a letter as follows . for a blank or empty sector * for a star E for the Enterprise K for a Klingon (an enemy vessel) B for a starbase. These letters are stored as a string S$ in the order corresponding to the number associated with the object. This means that S$ = ".*EKB" because the correspondence is as follows. 1 . for a blank or empty sector 2 * for a star 3 E for the Enterprise 4 K for a Klingon (an enemy vessel) 5 B for a starbase. In order to display the letter for the object, we have to pick the correct letter out of S$. For example, if S(I,J) = 4 the fourth letter in S$ which happens to be a "K" is to be displayed, because the number 4 in S(I,J) corresponds to the presence of a Klingon. Line 450 displays the corresponding letters by using the PRINT MID$(S$,N,L) function in the form PRINT MID$(S$,S(I,J),Z); " "; which operates as follows. The Z at the end (the number 1 corresponding to the 'L') tells the computer that a one character string long is to be displayed. S$ tells the computer which string to search for the letter. The starting location of the string to be displayed is set by the contents of S(I,J). Thus Copyright (c) Joe Kasser 1989 Chapter6 PAGE 5 STARTREK THE COMPUTER PROGRAM for each sector in the quadrant, the value of S(I,J) is determined. The letter corresponding to the number stored in the S(I,J) array is then displayed followed by a "space" character. The J loop repeats until the contents of all the sectors in a particular row have been displayed. At the end of the row, the cursor is moved to the position of the 20th character along the line by the PRINT TAB(20) ; statement. Note the use of the semi colon after both the MID$ and TAB print statements to stop the cursor advancing to the next line. If you look back to the example of the Short Range Sensor display, you will see that a different item of status information is displayed at the end of each line. Line 460 routes the computer to the correct item to be displayed by the use of the 'ON' statement. Lines 500 to 570 inclusive display the data elements. Since the value of the line counter (I), varies between 0 and 7, while the 'ON' statement requires a number equal to 1 or more, I+Z is used to convert the line count of 0-7 to the range of 1-8 needed for the ON statement. When the 'ON' statement is encountered the program flow branches to the destination specified by the order of the line numbers. In our case after the first row is displayed, when I+Z = 1, the program will branch to line 470. After the second row, to line 480, after the third row to line 490, and so on. Each of these lines are similar. They first display the name of the data element. The cursor position is then moved to the 38th character position along the line by the 'TAB(38);' statement and the contents of the actual element then displayed. After each element has been displayed the program flow branches forward to line 550 which increments the row loop counter, and when it times out, terminates the command function (subroutine). The variables used to store the game status items are as follows. T = The DAYS LEFT in the game C$ = The CONDITION of the Enterprise E1 = Energy in the SHIELDS E = The total ENERGY of the Enterprise P = The number of PHOTON TORPEDOES left B9 = The number of STARBASES remaining (multiplied by 10) K9 = The number of KLINGONS LEFT in the galaxy (multiplied by 10) K4 = The number of KLINGONS CAPTURED" Since both B9 and K9 are stored multiplied by 100, they have to be divided by 100 before being displayed, hence for example, the K9/100 in the PRINT statement of line 530. The subroutine to calculate and display the score begins at line 170 with the usual REMark statement. The score changes as a function of the time elapsed since the game started, the number of Klingons destroyed and the number of Klingons captured or suicided. Line 180 computes a value for the score and places it in the temporary variable 'N' using the statement Copyright (c) Joe Kasser 1989 Chapter6 PAGE 6 STARTREK THE COMPUTER PROGRAM 180 N=INT(((K8-K9)/100)*(K5/2.5+K4+Z)^2*100/(T9-T)) : IF N<0 THEN N=0 Consider the statement in sections. The number of Klingons destroyed is computed using the INT((K8-K9)/100) statement. The result is then divided by the elapsed time calculated in the (T9-T) statement. If the score was just a function of the number of enemy ships destroyed in the elapsed time so far, the value of N would be 180 N=INT(((K8-K9)/100)/(T9-T)). However a multiplier is put in to make capturing Klingons worth while even though they tend to damage the Enterprise during the capturing process. This multiplication factor is given by the statement (K5/2.5+K4+Z)^2*100 which represents one hundred time the square of the number of Klingons captured (K4) added to the number of Klingons that have suicided (K5) divided by two and a half. This complex multiplier generously rewards the player for taking the time and effort to capture Klingons and also gives a small amount of compensation for those that were destroyed by their own captain rather than be captured. If the value computed for N by the expression N=INT(((K8-K9)/100)*(K5/2.5+K4+Z)^2*100/(T9-T)) is negative, the value of N is set to zero by the statement IF N<0 THEN N=0 at the end of the line. Line 190 displays the score in a formatted position in the display using the 'PRINT "SCORE";TAB(38);N' statements and terminates the subroutine with the 'RETURN' statement at the end of the line. At this carefully time copy lines 400 to 550 and line 170 to 190 from figure 6.2 into your program and save it. Do not try to execute the Short Range Sensor command at this time. If you do, you will get error messages, because certain prerequisites have not been met. 6.2 The VISUAL Command Now would be a good time to look at the VISual command, since it essentially performs a subset of the Short Range Sensor command. The Visual command displays the contents of the sectors adjacent to the Enterprise. If the co-ordinates of the Enterprise in the Quadrant are S1 and S2 (ie S(S1,S2) = 3), then to display the contents of the adjacent sectors to the Enterprise the row and column loop counters just have to work on S1 and S2 plus or minus 1. The visual command is normally only used when the Short Range Sensors are damaged. Samples of the VISUAL command display are Copyright (c) Joe Kasser 1989 Chapter6 PAGE 7 STARTREK THE COMPUTER PROGRAM (a) . . . . . (b) . . . . . (c) $ $ . . . . . . . . . . . . . $ $ * * . . . E K . . B E K . $ $ E . . $ $ $ $ $ . . . . . $ $ . . . $ $ $ $ $ . . . . . $ $ . . . the first one (a) shows the Enterprise and a Klingon on the bottom row of the quadrant. The second (b) shows the Enterprise, a starbase and a Klingon somewhere in the middle sectors of the quadrant, and the last one (c) places the Enterprise in the first column of sectors. Two stars are also shown in the row above the Enterprise. The flow chart for the VISUAL command is shown in figure 6.3. The Visual command always works because you can always see out of the windows. The command is thus two loops for displaying the contents of the sectors adjacent to the Enterprise. Care must be taken so that sectors that are outside the quadrant are treated differently to sectors inside the quadrant. This is because the computer will output an error message if an attempt to access an illegal value of S(I,J) is made. and of course I and J will have illegal values for sectors outside the quadrant (ie less than 0 or greater than 7). These sectors are displayed as dollar signs to enable the player to locate the Enterprise within a quadrant should the Short Range Sensors be damaged. The Visual Command subroutine may be written in BASIC as shown in figure 6.4. It begins at line 2500 with the usual REMark statement. The heading is displayed when line 2510 invokes the subroutine starting at line 70. Two loops are invoked using a FOR/NEXT loop format as FOR I = S1-2 TO S1+2 : FOR J = S2-2 TO S2+2. Line 2520 tests to see if the sector whose contents are being displayed are inside the quadrant by using the logical 'OR' statement. The statement IF I<0 OR I>7 OR J<0 OR J>7 THEN will only be true if any one of the four conditions being tested are met. That is, if the value of I or J are less than 0 or greater than 7. If they are the 'PRINT "$"; : GOTO 2540' part of the line displays the dollar sign and advances the program past line 2530 which does the displaying of the letter associated with the contents of a sector as discussed above by means of the 'PRINT MID$(S$,S(I,J),Z);' statement. Line 2540 displays the "space" character then advances the column counter. After a row has been displayed, a 'PRINT' statement moves the cursor to the next line and the row counter is incremented. When that loop is terminated, the 'last command flag' (C9) is set to one to to inhibit line 3090 (in the main command loop) from moving any Klingons in the quadrant. The subroutine terminates at the Copyright (c) Joe Kasser 1989 Chapter6 PAGE 8 STARTREK THE COMPUTER PROGRAM RETURN statement. At this time carefully copy lines 2500 to 2540 from figure 6.4 into your computer program, don't forget to update the date in line 10, and save them. Again do not try to execute the command at this time or you will get error messages because before the contents of a quadrant can be displayed visually or as a short range radar display, they have to be set up first. The contents of the Q(I,J) array corresponding to a particular quadrant have to be transformed into values that can be used to position the different objects into various sectors. Consider the sample short range radar display shown above. There are two Klingons, no starbases and six stars in the Quadrant. The Quadrant co-ordinates are 4,6 so we know that Q(4,6) = 206. Thus before a Short Range Sensor command can be performed, that 206 has to be transformed so that the Klingons, stars and the Enterprise can be positioned in the various sectors within the quadrant. The flow chart to set up a new quadrant and position the objects within it is shown in figure 6.5. The first thing that is done is to clean up the quadrant by making all the sectors blank. This takes care of any previous contents of the array associated with any previous quadrant. The number of Klingons,starbases and stars in the quadrant are then computed. The Enterprise is then positioned in the quadrant followed by the Starbase if any, the stars and then the Klingons, again if any. If there are enemy ships in the quadrant, a 'RED ALERT' message is displayed. The program then checks to see if the player has put the shield up. If they are down, a message is displayed to that effect. The message is put out by the "Starfleet Command Training Simulator" part of the program. The BASIC language implementation of the flowchart could be as shown in figure 6.6. It begins at line 3200 with the customary REMark statement. Line 3210 then sets every sector in the quadrant to blank (ie it sets S(I,J) = 1). The real thing then begins at line 3220. Line 3220 tests for,and sets up the contents of, a quadrant that is outside the galaxy. By definition, there are no starbases or klingons outside the galaxy. There is also a remote possibility of the presence of a rogue star outside the galaxy. The test to see if the quadrant is inside the galaxy begins with the now familiar 'OR' test on the four requirements for being within the galaxy IF Q1<0 OR Q1>7 OR Q2<0 OR Q2>7 THEN if the test is true the program continues along the line. If the test is false, and the Enterprise is somewhere inside the galaxy, the program continues with the next line (line 3230). If the Enterprise is outside the galaxy, the Starbase and Klingon variables are set to zero by the statements K=0 : B=0 :. Copyright (c) Joe Kasser 1989 Chapter6 PAGE 9 STARTREK THE COMPUTER PROGRAM A random number between 0 and 1.199 is then computed and converted to an integer by the statement S=INT(RND(Z)*1.2). The probability of S being equal to one is thus quite low. The line terminates with the 'GOTO 3250' statement which bypasses the regular setting up code. Line 3230 uses N as a temporary variable. N is given the absolute value of the contents of the quadrant using the 'N = ABS(Q(Q1,Q2))' statement. Since the number of Klingons is equal to the hundreds digit, N can be divided by 100 to find out how many Klingons are in the Quadrant. Suppose for example the quadrant Q(Q1,Q2) = 306, there will be 3 Klingons, no starbases and 6 stars in the quadrant. N is thus 306. If N is divided by 100 it will have a value of 3.06. It is then converted to an integer (no decimal point) by using the INTeger function in BASIC. The statement thus used to find the value of the number of Klingons in the quadrant (represented by the variable K) is, 'K = INT(N/100)'. N is again used as a temporary variable in the detection of the presence of a starbase. The original value of N is the total contents of the quadrant. K is the number of Klingons. If the number of Klingons in the quadrant is multiplied by 100 and then subtracted from the original number, all that will be left is the number of stars and starbases. In our example we would see 306- 300 or 6. This function is performed in BASIC by the identity 'N = N - K*100'. The presence of a starbase can be detected in a number of ways. The technique used here is similar to that used to determine the number of Klingons, namely 'B = INT(N/10)'. This sets the value of 'B' to either '1' or '0' depending if a base is there or is not. An alternative method could be to test to see if N is greater than 10 and if so, set the value of B to 1, else make it a 0. That could be written in BASIC as IF N > 10 THEN B = Z ELSE B = 0. an approach that would lock the game into only having one starbase per quadrant. The technique used in line 3230 is more general and does not care how many bases are in the quadrant. Line 3240 computes the number of stars in the quadrant by subtracting the number of Klingons (multiplied by 100) and the number of starbases (multiplied by 10) from the original contents of the quadrant using the statement S = ABS(Q(Q1,Q2))-(K*100+B*10). It has to use the 'ABS(Q(Q1,Q2))' value because the value of N was changed by the operation that just preceded it and is no longer equal to the contents of the quadrant. Line 3250 invokes the subroutine beginning at line 50 to get two random numbers. The co-ordinates of the Enterprise within the quadrant (S1 and S2) are then set up. S1 is the row position and S2 the column position. The subroutine used X and Y as dummy variables for the purpose of communicating with the calling Copyright (c) Joe Kasser 1989 Chapter6 PAGE 10 STARTREK THE COMPUTER PROGRAM routine (the two numbers have to be passed somehow). We could have defined two special variable R1 and R2 for example, for this purpose, but did not. X and Y can be reused elsewhere in the program whenever a temporary variable is required. Reusing variables is a good idea in that it saves memory (since each variable occupies memory, and the more there are, the more memory is used). It is not a good idea in the sense that if you are not careful which and where variables are reused, strange things will happen when you un-intentionally re-use a variable. The contents of the quadrant occupied by the Enterprise are set to 3 by the 'S(X,Y) = 3' part of the line. The last part of the line tests to see if a starbase is present in the quadrant. if B = 0 then one is not and the program flow skips to line 3270. If one is, line 3260 positions it as follows. The random number generator subroutine that starts at line 50 is called. It returns two numbers (X and Y) which are now assumed to be the co-ordinates of the quadrant that the base is to be located in. If the contents of the quadrant are not equal to 1, ie the quadrant is not blank, a new random quadrant is chosen. If the quadrant is blank, it is set to 5, to signify the presence of the base. The BASIC language implementation of the operation is IF S(X,Y) <> Z THEN 32650 ELSE S(X,Y) = 5 where <> means "is not equal to". Literally is means, "is less than, or, is greater than". If a number is less than or greater than another number, they certainly cannot be equal. For each star in the quadrant, the FOR/NEXT loop in lines 3270 and 3280 locate a blank sector and position a star in it in a similar manner. The last part of line 3290 tests for the absence of Klingons. If the value of K = 0 then no Klingons are present in the quadrant and the program flow branches forward to line 3340. If there are Klingons in the quadrant, they are positioned in a likewise manner by the FOR/NEXT loop in lines 3300 to 3320. Line 3300 sets up the individual Klingon data. The row (K1(I)) and column (K2(I)) co-ordinates are first set up, and then the energy available to the Klingon is then calculated. All Klingons are given a random amount of energy between 0 and 999 units. The amount of energy is stored in the K3(I) array. The last part of the line displays a "RED ALERT" message using a FOR/NEXT loop to display the words "RED ALERT" three times using the statements 'FOR I = 0 TO 3 : PRINT "RED ALERT " : NEXT' The task could have been written using a different statement as shown below PRINT "RED ALERT RED ALERT RED ALERT". You will find many places where a particular task can be implemented in a number of ways, most of them equally correct. Line 3330 outputs a "beep" or tome to the terminal. The standard ASCII control character used to sound a bell tone at the console terminal is 7. The character is a non printing one. The 'CHR$(7)' function tells BASIC to output the control character 7 Copyright (c) Joe Kasser 1989 Chapter6 PAGE 11 STARTREK THE COMPUTER PROGRAM to the terminal. If you remember, CHR$(26) was used earlier to clear the screen. The last part of the line samples the amount of energy in the Shields. if it is zero, the shields are down and the player has moved the Enterprise into a quadrant containing enemy vessels. That is a definite NO-NO! A message to that effect is displayed. There is also a good probability as you will find later, that the Enterprise will be destroyed by the Klingons. Copy lines 3200 to 3340 from figure 6.6 into your computer program at this time and save it. Then try to RUN the program. The Visual and Short Range Sensor displays should work and show active displays. The CONDITION will be blank because C$ has not yet been set up. If your program is not performing correctly and you are getting error messages, debug it and eliminate them at this time, then save the corrected or debugged version of the program. Add a temporary line or statement to define C$ = "DEBUG" in case the absence of a defined value for C$ is bothering your computer. A static display like this is dull so lets fudge a move command to position the Enterprise in different quadrants. For debugging, we can put in a temporary move command as shown below which will allow different quadrants to be scanned. 1300 REM NAV WARP ENGINES/NAVIGATION 1310 1305 GOSUB 50 : Q1 = X : Q2 = Y : GOSUB 3200 1315 PRINT "MOVED TO QUADRANT ";Q1+Z;",";Q2+Z 1750 RETURN These lines perform a "move" operation on the Enterprise by relocating it at random throughout the galaxy each time the Move command is invoked. Note the use of numbers ending in 5 signifying by our convention that they are temporary lines to be deleted later. These lines are inserted following line 1300. Line 1310 is left blank. Just enter the line number followed by a carriage return. This procedure will delete the current line 1310 which contains a 'GOTO 1000' instruction. Line 1605 uses the random number subroutine to set up the Galactic Quadrant co-ordinates (Q1 and Q2) of the Enterprise. The set up subroutine of line 3200 is then invoked to position the contents of the quadrant in the relevant sectors. The variables Q1 and Q2 are used to remember in which quadrant the Enterprise is located at any stage of the game, in a similar manner to the use of S1 and S2 to note which sector inside a quadrant the Enterprise is occupying. Q1 and Q2 are important when moving the Enterprise around the galaxy and S1 and S2 are important when things will begin to happen inside the quadrant. Line 1615 displays a message that the Enterprise has moved and also displays the destination. The +Z in the PRINT statement is used to convert the 0-7 co-ordinates that the computer uses tot he 1-8 that the player uses. The point has been discussed Copyright (c) Joe Kasser 1989 Chapter6 PAGE 12 STARTREK THE COMPUTER PROGRAM earlier. The subroutine terminates at line 1625. Enter lines 1605 to 1625 and run the program. You should now be able to move the Enterprise around the galaxy and get different displays when executing the Short Range Sensor, Visual, Map and Long Range Sensor commands while moving around the different quadrants in the galaxy. Stop the program execution (^C) and enter D(5) = 2. Then let the program CONTinue. You will now find that the Map does not work. The computer is down. Move to a new quadrant and to a Long Range Sensor Scan. Then use the Damage Control to repair the computer and try the Map display again. If all has gone well, you will find that the information about the quadrant that the Enterprise is currently located in has not been entered into the Map. If it has, you either have a bug in your version of the Program, or the data was entered by a previous Long Range Sensor scan. Stop the program, enter D(5) = 2 and move again. Now exercise the Map, repair the computer and try the map again. The map should not show the contents of the Enterprise's quadrant. Do a Long Range Sensor scan and then a Map command. The map should now be updated. At this time, a lot has been accomplished. All that is left as far as the quadrant is concerned is to set up the Condition (C$), ie determine the Condition of the starship. If you remember the condition was defined as follows. RED Battle area, enemy in quadrant YELLOW One of the sub-systems aboard the Enterprise is damaged, or the Energy level has fallen to below 400 units. GREEN Everything is fine, no enemy detected, damage, and sufficient energy aboard the ship. The flow chart to determine the condition of the Enterprise is shown in figure 6.7. The first thing that happens is that the contents of the sectors adjacent to the Enterprise are sampled to see if the Enterprise is located next to a starbase. If the Enterprise is located in a sector adjacent to a base, then a further test is performed to see if the Enterprise is already docked. If the Enterprise is already docked, the parameters (Energy and Photon Torpedoes) are reset to their initial values. This allows the player to blast away at any Klingons in the sector while the Base continually resupplies the ship. If the Enterprise is not yet docked, then a test is performed to determine if any Klingons are in the quadrant. If there are, there is a possibility that the starbase will not be able to lower its shields (presumably it is also under attack by the enemy) to allow the Enterprise to dock. This possibility is set at 50%. Thus if there are Klingons in the quadrant, there is a 50% probability that the Enterprise will not be able to dock. Copyright (c) Joe Kasser 1989 Chapter6 PAGE 13 STARTREK THE COMPUTER PROGRAM Its too bad if you are badly hit and are limping home to base with the Klingons firing at you. If you are really unlucky they might even destroy the Enterprise while it is waiting to dock. The docking procedure, displays a message that docking is taking place, deducts half a stardate from the time left in the game and updates the ship's Energy and weapon parameters. The condition of the ship is also set to "DOCKED" at this time. On the other hand, if the Enterprise is not located in a quadrant that is adjacent to a base, the program first tests to see if any Klingons are present in the quadrant. If they are, the condition is set to "RED". If no Klingons are there, then the condition can be either "YELLOW" or "GREEN". The condition can be "YELLOW" if one of the subsystems is damaged, or if the total remaining energy aboard the Enterprise is less than 400 units (10% of the initial value). If either of those conditions are met, the condition is set to YELLOW. If none are met, all is assumed to be OK and the condition is set to "GREEN". The BASIC language implementation of the flowchart is as shown in figure 6.8. The subroutine begins at line 3400 with the usual REMark. Line 3410 commences two loops that perform the sector scan. The technique used is almost the same as that used in the Visual command. Here instead of accepting what ever is in the sector, we just need to know if one contains a base. The row and column loops scan one sector in each side of the Enterprise, including the one occupied by the Enterprise itself. We know that that test will fail, but so what? The search routine is simplified if we can treat all sectors in the same way. We thus just performs a continuous scan on nine sectors (three per row). Line 3420 checks to see if a sector is outside the quadrant. If it is the program skips forward to line 3440 bypassing line 3430 which does the actual test to see if the sector contains a Starbase using the statement IF S(I,J) = 5 THEN 3450. If the sector does contain a base, the loop is terminated by the branch to line 3450. The test is skipped for sectors outside the galaxy because S(I,J) is invalid if I or J are less than 0 or greater than 7. Line 3440 terminates the loops and then directs the program to continue at line 3490 in the event that a Starbase was not found. If a base was located, the program picks up at line 3450 which tests to see if the Enterprise is already docked. The value of C$ is used as the condition flag. If it is "DOCKED" then the Enterprise is already docked and the parameters are updated using the subroutine starting at line 90 and repairs all the subsystems by calling the subroutine starting at line 3550 which sets all sub-systems to "working" (D(I)=0). The routine then branches forward to line 3540. It is simpler to just set all the sub-systems to zero rather Copyright (c) Joe Kasser 1989 Chapter6 PAGE 14 STARTREK THE COMPUTER PROGRAM than test each one and set it to zero if it is non zero. The computer is fast, the player will never notice the difference in execution time between the two different methods. Setting them all to zero irrespective of the way way they were results in them all being zero, and that is what we want. Programs should use the "KISS" principle as well as being structured. KISS by the way is an acronym for KEEP IT SIMPLE STUPID. If the Enterprise is not docked, line 3460 tests to see if there are any Klingons in the Quadrant. The test statement includes the logical 'AND' statement. This means that both test conditions have to true before the program will continue at the line number specified by the 'THEN' part of the test. The first part of the test (IF K>0 ) tests to see if the number of Klingons in the sector is greater than zero. If it is, then there are enemy vessels in the quadrant. At this time, their numbers do not matter. The second part of the test (RND(Z) < .5 ) uses the random number function built into BASIC to generate a random number between 0 and 0.99999. The number is then compared with a constant (0.5). If the random number is less than 0.5 (a 50% probability), the test is true and the program flow continues at line 3490. Note that if the first test fails, Microsoft BASIC will ignore the second test and continue program execution at the next line number. The docking procedure begins at line 3470. The first thing that happens, is that a message is displayed telling the player that the Enterprise is docking. The display message is in two parts. D$(6) is used to save space in the program source code. We have previously defined D$(6) to contain the word "SHIELDS " (see line 4580). Then the subroutine starting at line 3550 is invoked to repair all of the on-board sub-systems. Once the systems are repaired, a message to that effect is displayed at the console by the last part of the line. Line 3480 invokes the parameter updating subroutine starting at line 90, then subtracts half a stardate from the game time remaining ( T = T - .5 ) and sets the value of C$ to "DOCKED". The program flow then branches forward to line 3540. Line 3490 is where we pick up if the Enterprise is not located adjacent to a starbase. It tests the value of K to determine if any of the enemy are present in the quadrant. If the value of K is greater than zero, namely there is at least one Klingon in the quadrant, then C$ is set to "RED" and the program skips to line 3540. If there aren't any Klingons in the quadrant, then the program continues at line 3500. Line 3500 examines the state of the sub-systems using a FOR/NEXT loop. If any sub-system has a value of D(I) greater than 0, it is damaged. The contents of C$ are set to "YELLOW" and the program flow leaves the loop by GOing TO line 3540. We don't care which one is damaged, we only care if any one of them is. If the test fails, then all the subsystems are in working Copyright (c) Joe Kasser 1989 Chapter6 PAGE 15 STARTREK THE COMPUTER PROGRAM order, and the loop times out naturally. The program then tests the amount of Energy remaining aboard the starship to see if it is less than 10% of the initial value. If it is, the contents of C$ are also set to "YELLOW" else the amount of energy is greater than 10% of the initial value, (and nothing is damaged) and the contents of C$ are set to "GREEN". The subroutine terminates at line 3440. This subroutine has itself called two subroutines, one at line 90, the second at line 3550. When one subroutine calls an other the second subroutine is called a "nested" subroutine. The terminology is the same as that used to refer to loops. Copy lines 3400 to 3540 from figure 6.8 into your program, check your spelling, then SAVE it and RUN it. The game should behave as before, but now, the condition should show up as "RED" or "GREEN" depending on the presence or absence of Klingons in the quadrant. Break the program and set the amount of energy to less than 400 units (enter E = 200 for example). CONTinue the program and see if the condition changes between YELLOW and RED. Stop the program (^C again), re RUN it and this time break it and damage a subsystem (enter D(I) = 3, where I is the number of your choice). Now again test that the condition varies between YELLOW and RED. Repair the damaged sub-system and verify that the condition now changes between GREEN and RED. At this time save the program because it should be working properly. Delete line 1305 and 1315 so as to avoid any trouble when the real "MOV" command is implemented. At this time the program should be as shown in figure 6.9. Once the Short Range Sensors and the Visual commands have been programmed, the next stage is to implement the real move command. Copyright (c) Joe Kasser 1989