l Program

In the first lesson, you learned to use setMove() and setTurn() to make the Finch move in a straight line and turn in place. But there are a lot of other ways the Finch can move! What if you want the Finch to draw a figure-8 or move in a large circle?

To get a wider range of movements, you can use setMotors() to set the speed of each wheel individually. This method takes two parameters, which are the speed of the left and right wheels.

To move the Finch using setMotors, you must turn the wheels on, pause the program, and then turn the wheels off. Sample code is shown below. This code moves the robot forward for one second. Note that you could also use setMotors(0,0) or stopAll() to turn off the motors.

In Exercise 2, you probably just assumed that the user entered speeds between -100 and 100, but it is a good idea to check whether the user entered valid values. You can do this with an if-else statement. An if-else statement enables your program to make a decision. For example, suppose you want to turn on the Finch’s motors for a certain number of seconds. First, you ask the user for input. Then you turn one motor on for that amount of time. Note that this code will allow the user to enter a decimal number.

However, this code will have an error if the user enters a negative number (try it!). Before you set the beak and pause, you want to check if time is less than zero. The code below shows how to do this with an if-else statement. The keyword if is followed by a comparison in parentheses, time < 0. This comparison is a Boolean expression, which means that it is either true or false. If the comparison is true, the program runs all the lines of code inside the curly braces {} that follow the if. If the comparison is false, the program runs all the lines of code inside the curly braces that follow the else. Then the program moves on to the next line following the if-else statement. In this case, if time is less than zero, the program prints an error message. Otherwise, it turns the Finch for time seconds.

Sometimes you want to check whether two Boolean statements are true. For example, in Exercise 2, it would have been helpful to check whether the speed was greater than or equal to -100 and less than or equal to 100. You can do this with the logical and operator &&. The Boolean expression below is true if BOTH of the statements in parentheses are true. Otherwise, it is false. 

The logical or operator || or is slightly different. The Boolean expression below is true if EITHER of the statements in parentheses are true. It is false when both statements are false.