robotc software introduction. robotc software robotc developed specifically for classrooms and...
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ROBOTC Software
Introduction
ROBOTC Software
• ROBOTC developed specifically for classrooms and competitions
• Complete programming solution for VEX Cortex and several other popular robot platforms
• Real-time debugger• Similar to industry-standard C programming
Industry Standard Coding
• ROBOTC programming is a key components of industry standard programming languages
Sample Program
// sample comments to describe behaviortask main(){ startMotor(rightMotor, 63); wait(); stopMotor(rightMotor);}
Statements and Expressions
• Statements are the smallest complete unit of a working program.
• Statements primarily consist of expressions, keywords and operators
• Expressions may consist of keywords, operators, values, variables, etc.
• Example:int length = 2 * 12; // convert feet to inches
Comments
• Comments are used to make notes in code for the human programmers
• Every sample program contains comments pertaining to robot configuration, ROBOTC commands, robot behavior, etc.
• // Single line comment – All material after “//” is ignored by the ROBOTC compiler
• /* Multi-line comment*/ – All material between the “/*” and “*/” symbols is ignored by the ROBOTC compiler
Keywords
• Keywords are specific directives that mean something special to the ROBOTC compiler
• They are sometimes called reserved words because the compiler “reserves” those words and they can not be used for any other purpose.
• Some keywords you will see: #pragma, task,
Operators
• Similar in behavior to a mathematical function: Examples: 1 + 2 or ADD(1,2)
• They commonly take one or more operands and produce a result
• Foundational to building expressions and statements
Simplified Order of OperationsOrder Operator(s) Notes
1 () [] -> . :: Grouping, Scope, Array
2 ++ -- increment/decrement*
3 * / % Multiply, divide, modulo
4 + - Addition, subtraction
5 < <= > >= Comparison
6 == != Comparison
7 && Logical AND
8 || Logical OR
9 = += -= *= /= %= Assignment
More info: http://en.wikipedia.org/wiki/Order_of_operations*Note: this also depends on pre versus post behavior
Variables
• A variable is a special form of a label that allows you to reference a value in memory by a name instead of just a location
• Variables are “variable” by nature – their contents can usually be changed
• Variables can improve the readability and expandability of your programs
• To change the value of variable:int distance = 500; // declare and set
Creating a Variable• Declare the variable (stating its type and its
name) once at the beginning of task main:
Type of data:• int• float Name of variable:
• Starts with letter• Letters, numbers, and
underscores are ok• Not a reserved word
Variable Types
Data Type Description Example Code
Integer Positive and negative whole numbers, as well as zero
-35, -1, 0, 33, 100
int
Floating Point Number
Numeric values with decimal points (even if the decimal part is zero)
-.123, 0.56, 3.0, 1000.07
float
Boolean True or false – Useful for expressing the outcomes of comparisons
true, false bool
Character Individual characters, placed in single quotes. Not useful with POE kits.
‘L’, ‘f’, ‘8’ char
String Strings of characters, such as words and sentences placed in double quotes. Not useful with POE kits.
“Hello World!”, “asdf”
string
Assigning a Value to a Variable• The assignment operator is the single
equal sign• The right-hand side of the equal sign is
evaluated, and then the value is assigned to variable on the left-hand side
• This is not the equality from algebra!Declaration
Initialization
Assignment
Assignment
Variable Applications
• Variables are needed for most programs. Here are some examples:• Example #1: Repeat code 5 times• Example #2: Count user’s button presses• Example #3: Remember if the user EVER
pushed a button• Example #4: Remember a maximum value• Example #5: Debug a program by
remembering which branch of code has been executed.
Global vs. Local Variables
• Variables can have either a “global” or a “local” scope.– Global variable
• Can be read or changed from any task or function in your code.
• Its value can be seen/read globally.
– Local variable• Belongs only to the task or function in which it was created• Value can only be read or changed from within that task or
function• Value can only be seen/read locally• Generally the type of variable you’ll want to use, local to
“main”
Functions
• Functions– Group together several lines of code– Referenced many times in task main or in other
functions
• Creating Functions
Example: LED on if bumper is pressed, off if released
1. Function header (name of function)
2. Function definition (code in the function)
3. Function call (where function code will run)
Function Definition
• Function definitions define the code that belongs to the function
Function Call
• Function calls– Call and run code from function– Placed in task main or other functions
While Loops
• While loop is a structure within ROBOTC• Allows a section of code to be repeated as long
as a certain condition remains true
• Three main parts to every while loop1. The word “while”
2. The condition
3. Commands to be repeated
2. The Condition
• Condition is an expression that controls how many times a while loop repeats– When condition is true, the while loop repeats– When condition is false, the while loop ends
and the remainder of the program executes
• Condition is checked once every time loop repeats before commands between curly braces are run
Boolean Logic
• Program decisions are always based on questions
• Only two possible answers– yes or no– true or false
• Statements that can be only true or false are called Boolean statements
• Their true-or-false value is called a truth value.
Boolean Logic
Writing a condition: Example• While the bump switch is not pressed:
wait until it’s dark, then turn on light;
wait until it’s light, then turn off light
Timers
• Loop control– Where would the wait statement go if we
wanted the loop to repeat for a controlled amount of time?
– Nowhere! We need something else.• Solution: Timers
– Internal stopwatches (4 available)– Like encoders, timers should be cleared
before they are used– Be careful: don’t clear a timer in a timed loop
TimersTimer T1 is used as the condition for the while loop, which will run for 30 seconds
If Statements
• If statement in the program is evaluated by condition contained in parentheses– If condition is true, commands between
braces are run– If condition is false, those commands are
ignored• Very similar to how a while loop works, but
does not repeat the code
If-Else Statements
• If-else statement is an expansion of if statement– If checks condition and runs appropriate
commands when it evaluates to true– Else allows code to run when condition is
false– Either if or else branch is always run once
Multiple If-Else Statements
• Be careful when using two separate if-else statements, particularly if both are used to control the same mechanism
• One branch of each if-else statement is always run so that you may create a scenario where the two statements ‘fight’ one another
Behavior-Based Programming• A behavior is anything your robot does
– Turning on a single motor or servo
• Three main types of behaviors 1. Complex behaviors – Robot performs a complex
task (automated fan control)
2. Simple behaviors – Simple task performed by the robot (fan stops when sensor activated)
3. Basic behaviors – Single commands to the robot (turn on a motor)
• Complex behaviors can always be broken down into simple behaviors, which are then broken down into basic behaviors
Program Design
• Many basic behaviors generally come together to create a complex behavior.
• Troubleshoot basic behaviors as they come together to form a complex behavior.
Complex Behaviors
• Describe the task or overall goal that your program will accomplish.– A fan will run until someone
needs it to stop. A safety device warning light will come on before the fan turns on. Another light will indicate that the fan has stopped.
• This may be described as one or more complex behaviors.
Simple Behaviors
• Break each complex behavior down into simple behaviors.
• List the behaviors line by line in the order that each should occur.
• Describe actions and what prompts each action to continue.
Basic Behaviors
• Break each simple behavior down further into basic behaviors.
• Think in terms of what each input and output component will be on your device.
Program Design
• Code and test small behaviors or sets of behaviors individually.
• Edit or add comments as you build code.
Program Design
• Continue programming while testing one behavior at a time.– Temporarily turn sections of code into
comments using /* followed by */.