Transcript Syntax-07-08-29 - Tulane University

More switches, Comparison
Day 7
Computer Programming
through Robotics
CPST 410
Summer 2009
Course organization
 Course home page
(http://robolab.tulane.edu/CPST410/)
 Lab (Newcomb 442) will be open for
practice with 3-4 Macs, but you can bring
your own laptop and all robots.
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Review
More than two choices
 Tribot, when I press the left NXT button,
pick a number from 1 to 3.
 If the number is 1, display an image.
 If the number is 2, beep.
 If the number is 3, play a sound.
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Switch3.rbt
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Switches in NXC
 A switch statement can be used to execute
one of several different blocks of code
depending on the value of an expression.
 It has the following syntax:
switch (expression) body
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Case labels
 One or more case labels precede each block
of code.
 The labels are not statements in themselves
- they are labels that precede statements.
 They have the following syntax:
case constant_expression :
default :
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Example
the number of each case is a value of x
int x;
…
switch(x)
{
case 1:
// do something when x is 1
break;
case 2:
case 3:
// do something else when x is 2 or 3
break;
default:
// do this when x is not 1, 2, or 3
break;
}
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More on case labels
 Each case must be a constant and unique within
the switch statement.
 The switch statement evaluates the expression
then looks for a matching case label.
 It will then execute any statements following the
matching case until either a break statement or the
end of the switch is reached.
 A single default label may also be used - it will
match any value not already appearing in a case
label.
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So now do the task in NXC
 Tribot, when I press the left NXT button,
pick a number from 1 to 3.
 If the number is 1, display an image.
 If the number is 2, beep.
 If the number is 3, play a sound.
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First try: just the switch
int num;
task main()
{
num = Random(3); // Random starts at 0
switch(num)
{
case 0:
GraphicOut(“Smile 01.ric”);
Wait(1000);
break;
case 1:
PlayTone(440, 500):
Wait(500);
break;
case 2:
PlayFile(“Laughing 02.rso”):
Wait(500);
break;
}
}
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The switch in a while loop
int num;
task main()
{
while (SensorBoolean(S1) == true) // touch sensor on port S1
{
num = Random(3);
switch(num)
{
// Random starts at 0
case 0:
GraphicOut(“faceopen.ric”);
Wait(1000);
ResetScreen(); // otherwise graphic never goes away
break;
case 1:
PlayTone(440, 500);
Wait(500);
break;
case 2:
PlayFile(“Laughing 02.rso”);
Wait(500);
break;
}
}
}
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Comparison
Kelly §15
The challenge
 Tribot,
1. choose two numbers randomly between 0 and
9 (call them A and B),
2. and display them on the screen.
3. Then, if A is greater than B, display “true”;
otherwise, display “false”.
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ComparisonTest1.rbt
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Combining text
 We now have two numbers to display, but a
DISPLAY block can only display one at a
time.
 Thus the two numbers have to be combined
or concatenated into a single bit of text.
 The TEXT block does this.
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The TEXT block
 Drag a TEXT block out of
the Advanced palette - it
has the icon “a”.
 Pull out its hub all the
way:
 It has inputs for 3 pieces of
text,
 or text can be written in the
settings windows.
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Display the two numbers
 Drop a TEXT block at the end.
 Plug textualized number A into TEXT plug A.
 Plug textualized number B into TEXT plug C.
 Enter ” > " into the text box of TEXT plug B.
 Drop a DISPLAY block after the TEXT block.
 Connect the TEXT block to it via the Text plugs.
 Raise the text to line 3.
 Don’t forget to WAIT for the display!
 Test the program.
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ComparisonTest2.rbt
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Now, the comparison
 This program gives a dumb result whenever
A is less than or equal to B.
 As a first step towards making it less dumb,
let us examine the COMPARE block.
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The COMPARE block
 Pull out a COMPARE
block (it has > = <)
from the Data part of
the Complete palette.
 It has three operations:
 less than,
 greater than,
 equals.
 And two input hubs.
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Adding the comparison
 Drop a COMPARE block at the end of the
sequence bar.
Set it to ‘>’.
Where should its inputs come from?
From the number outputs of the two Number to Text
blocks.
see the next slide
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ComparisonTest3.rbt
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Now, a decision
 But we want to display "True" if the comparison is true,
and "False" otherwise.
 How do we do that?
 Drop a SWITCH block at the end of the sequence bar.
 Set it to tabbed view, for convenience.
 Set Control to Value.
 Run a wire from the COMPARE Logic plug to the SWITCH input
plug.
 Now fill in each condition with a DISPLAY block with the
appropriate text on line 6, and don’t clear the screen.
 Don’t forget to add a WAIT at the end!
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ComparisonTest4.rbt
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Play with it
Next time
 Comparison in NXC.
 The RANGE and LOGIC blocks.
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