FSHS Robotics C Course

2. Basics of RobotC

2.1 RobotC Introduction

Now that we've learnt a tiny bit of C, let's quickly look at RobotC. Everything in the table from 1.2 is the same, except:

Code	RobotC Code	Comment
`#include <stdio.h>`	-	Not needed! Instead, some automatically generated code replaces this.
`int main() { ... }`	`task main() { ... }`	Instead of returning an int, we call them 'tasks'.
`return 0`	-	Tasks do not require return values.

2.2 Moving motors in RobotC

Let's look at a program that runs Motor A for one second, then stops.

#pragma config(Motor, motorA, motorL, tmotorNXT, PIDControl, encoder)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

task main() {
    motor[motorL] = 100; // SETS the motor speed
    wait1Msec(1000); // Keeps running at 100 speed for 1 second
    motor[motorL] = 0; // sets speed to 0
}

Key things to note:

C reads top to bottom. So, the motor is set to 100, nothing happens for 1 second, then it stops.
The = makes a change to a particular variable. Here, it's changing the motor speed variable.
The 1000 in wait1Msec(1000) is an argument to the wait function. We can change this number if we want it to be longer or shorter.
The motor speed is set. It isn't 'pinged' - from the point you call motor[motorL] = 100, it will run at 100 speed forever until it is stopped or the program terminates.

2.3 Exercises

Given the following starting code, copy the code into a new file, call it simplemotor.c and save it in your Robotics folder.

#pragma config(Motor, motorA, motorL, tmotorNXT, PIDControl, encoder)
#pragma config(Motor, motorB, motorR, tmotorNXT, PIDControl, encoder)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

task main() {
    motor[motorL] = 30;  // SETS the left motor speed
    motor[motorR] = -30; // SETS the right motor speed to go backwards
    wait1Msec(1000);     // Keeps running for 1 second
    motor[motorL] = 0;   // sets speed to 0
    motor[motorR] = 0;   // sets speed to 0
}

What do you think the code does? If it was hooked to a robot with two wheels, what would the robot do?
Change the code so that the robot goes forward for 1 second, spin clockwise for 3 seconds, moves backwards for 1 second and then stops.

Ask for the code to be uploaded to a demo robot and see if it works!

Basics of C Variables