1. Writing IC functions that depend on information from the outside
  2. Printing

Writing IC functions that depend on information from the outside

You have seen how to write simple functions in Interactive C. Now say that someone asks you to do the following: write a function that will make the robot move forward for n seconds. You can assume that LEFT_MOTOR and RIGHT_MOTOR refer to the left and right motor ports, respectively. You can accomplish your task as follows: 
void forward_for_n(float n) {
   forward(); /* note that you can call any function from within another */
   sleep(n);
   ao();
}

void forward( ) {
   fd(LEFT_MOTOR);
   fd(RIGHT_MOTOR);
}
In the function forward_for_n, "n" is a placeholder for a specific value that we expect someone to supply when the function is actually needed. Note the function header: 
void forward_for_n(float n)
Inside of the parentheses we include the declaration 
float n
This tells Interactive C that when the function is called, the caller will supply a value and the value is expected to be a real number.

To use the function (say, to make a robot go forward for 3 seconds), all you need to do is supply the value 3.0 in parentheses: 

forward_for_n(3.0);
We call "n" in the example above a formal parameter. We say that 3.0 is an actual parameter.

The syntax for supplying an actual parameter to a function should seem familiar, as you've seen it in the fd, bk, motor, and sleep function, among others.

Printing

Many of the programs we use print information on the computer screen: email programs print actual email messages; spreadsheet programs print results of computations; many programs print error messages when we try to use them incorrectly.

All messages are printed to the LCD on the Handy Board. We can print cute messages like "I am a happy handy board" (recall Lab 2). We can also print status information that might be useful in debugging our programs.

To print a message such as "I'm printing...":

printf("I'm printing...\n");

This will print I'm printing... with a newline (i.e., return) at the end.

Recall our program from last time: 

/* A. Danyluk */
/* September 2006 */

int LEFT_MOTOR = 3;     /* the left motor port */
int RIGHT_MOTOR = 1;    /* the right motor port */

/* Move forward, spin a bit, straighten out, then slow to a stop */
/* when the stop button is pressed. */
void main( ) {
   start_press();
   forward();
   sleep(3.0);
   spin_a_bit();
   forward();
   stop_press();
   slow_stop();
}

/* Move forward */
void forward( ) {
   fd(RIGHT_MOTOR);
   fd(LEFT_MOTOR);
}

/* Spin for 5 seconds */
void spin_a_bit( ) {
   fd(LEFT_MOTOR);
   bk(RIGHT_MOTOR);
   sleep(5.0);
   off(LEFT_MOTOR);
   off(RIGHT_MOTOR);
}

/* Slow to a stop */
void slow_stop( ) {
   motor(RIGHT_MOTOR, 20);
   motor(LEFT_MOTOR, 20);
   sleep(5.0);
   off(RIGHT_MOTOR);
   off(LEFT_MOTOR);
}
Let's modify it by adding a printf at the beginning of each function: 
/* A. Danyluk */
/* September 2006 */

int LEFT_MOTOR = 3;     /* the left motor port */
int RIGHT_MOTOR = 1;    /* the right motor port */

/* Move forward, spin a bit, straighten out, then slow to a stop */
/* when the stop button is pressed. */
void main( ) {
   printf("Starting main\n");
   start_press();
   forward();
   sleep(3.0);
   spin_a_bit();
   forward();
   stop_press();
   slow_stop();
}

/* Move forward */
void forward( ) {
   printf("In function forward\n");
   fd(RIGHT_MOTOR);
   fd(LEFT_MOTOR);
}

/* Spin for 5 seconds */
void spin_a_bit( ) {
   printf("In function spin_a_bit\n");
   fd(LEFT_MOTOR);
   bk(RIGHT_MOTOR);
   sleep(5.0);
   off(LEFT_MOTOR);
   off(RIGHT_MOTOR);
}

/* Slow to a stop */
void slow_stop( ) {
   printf("In function slow_stop\n");
   motor(RIGHT_MOTOR, 20);
   motor(LEFT_MOTOR, 20);
   sleep(5.0);
   off(RIGHT_MOTOR);
   off(LEFT_MOTOR);
}
Now as the program runs, the LCD will display where we are in the execution of the program. This is generally not necessary in short programs, but can be very useful when we're trying to debug a large, complex program and want to pinpoint where the program fails.

In addition to printing messages, we can print values -- for example, sensor readings, results of computations, etc.

To print the value of a sensor - for instance, the value of the digital sensor in port 8:

printf("%d\n", digital(8));

To print a message and a value:

printf("Digital %d is %d\n", 10, digital(10));

prints Digital 10 is 0

if the value of digital sensor 10 is 0

In summary: