Preprocessor Directives last modified 91905 2:47pm

1
Preprocessor Directives(last modified 9/19/05
247pm)

• Statements beginning with are directives to the
  preprocessor.
• They DO NOT end with
• Before the program is compiled, the preprocssor
  copies these definitions into the code.
• These definitions are not required, but make the
  code easier to write and more readable
• if you want to change the port on which a sensor
  is connected, and that appears multiple times in
  the program, then a single change in the define
  is all you need to make the change.

2
// tankbot2.nqc - drive and turn //
motors define LEFT OUT_A define RIGHT OUT_C //
how much time to spend turning or forward define
TURN_TIME 200 define STRAIGHT_TIME
100 // speed to run a turned motor define
TURN_POWER 3 task main() // start with
both motors on On(LEFTRIGHT) // repeat
the following steps forever while(true)

3
Programming Style

• Use indentation to visually group program blocks.
• Use comments to document the program

4
// tankbot2.nqc - drive and turn //
motors define LEFT OUT_A task main()
// start with both motors on
On(LEFTRIGHT) // repeat the following steps
forever while(true) // turn
right by slowing down the right tread
SetPower(RIGHT, TURN_POWER)
Wait(TURN_TIME) // resume going
straight SetPower(RIGHT, OUT_FULL)
Wait(STRAIGHT_TIME) // turn left
SetPower(LEFT, TURN_POWER)
Wait(TURN_TIME) // resume going
straight SetPower(LEFT, OUT_FULL)
Wait(STRAIGHT_TIME)
5
Time

• NQC is a real-time programming language.
• Time is measured in 1/100 of a second
• define TURN_TIME 200
• Will define the turning time to be 2 seconds

6
Using Time to Control Motion

• Wait(300)
• The program will wait at that statement for 3
  seconds.
• The following program will drive straight for 4
  seconds, then if OUT_A is attached to the left
  tread, the left tread will stop and the right
  tread will continue to drive for 1second causing
  the tankbot to stear toward the left.
• On(OUT_A OUT_B)
• Wait(400)
• Off(OUT_A)
• Wait(100)

7
Generating a Random Number

• NQC has a random number generating function
• Random(100)
• Generates a random integer between 0 and 100.
  All numbers in the range are equally likely
  (uniform distribution)

0
100
8
NQC Functions

• So far we have seen several NQC functions. They
  have been associated with
• Motors
• On(arguments)
• Off(arguments)
• SetPower(arguments)
• OnFwd(arguments)
• Sensors
• SetSensor(arguments)
• Mathematical
• Random(arguments)

9

• All NQC functions begin with a capital letter.
  As in SetSensor, two capitals are used to make
  them more readable.
• The number of arguments depend on the function.
• Appendix D (Braun) provides a Quick Reference to
  the language. The functions are grouped into
  categories. NOTE the restrictions. NOTE THERE
  ARE A FEW DIFFERENCES BETWEEN RCX AND RCX2.0.
  Which system do you have?