Introduction to Programming

1
Introduction to Programming

• MVRT 115

2

• This is an introduction to programming in the C
  language.
• We will be working on Vex and NXT robots, and
  later on
• the large robot.
• In this class, we assume that you know little or
• nothing about programming in general.
• If you have programmed in C, C, or Java, or
• if you were programming on the team last year,
• there will be a different class for you.
• In the advanced class, we will be working on the
  sensors and camera.
• We will talk about style, efficiency, testing and
  debugging.

3
Just the Basics

• A computer is an electronic machine that can do a
  limited number of things, like adding,
  subtracting, multiplying, dividing, or comparing
  two numbers.
• A computer can input numbers from keyboards,
  disk drives, and sensors. The computer can output
  numbers to a computer screen, a disk, a printer,
  or a motor.
• Input output is collectively referred to as
  I/O.
• Computer instructions are done in sequence, one
  after the other until the last instruction is
  executed then the computer stops.
• A set of computer instructions is known as a
  program.
• Numbers can be stored ( retrieved) from a
  computers memory.
• We say a program runs or executes. We can perform
  or execute an instruction

4
Programming Languges

• C
• C
• Java

5
Programming Languages

• Programming in machine language is tedious
  error-prone for humans.
• Computer memory locations are numbers. E.g., the
  first 256 bytes of memory are locations 0 through
  255. (Everything on computers starts counting at
  zero.)
• For example, to add two numbers in memory
  locations 150 and 200
• Get the first number from memory location 150
• Get the second number from memory location 200
• Add the two numbers together
• Store the addition result in memory (maybe
  location 204)

6
Programming Languages

• Programming languages, like C Java, make things
  easier adding two numbers can be done in one
  line of C, and you dont have to know memory
  locations!, e.g., sum a b
• A bit is a single binary digit either 0 or 1.
• A byte is a set of 8 binary digits and can
  represent 256 different values.

7
The Most Important Thing

• The most important thing to know about
  programming is that computers do what you tell
  them to do.
• Not what you youd like them to do.
• Not what you think they should do.
• You must know how to translate what you want
  into a form the computer can use.
• The syntax must be correct.
• The logic must be correct.
• When the computer does something wrong, its
  almost certain that you programmed it to do the
  wrong thing.

8
Basic Programming Form

• Every program must contain zero or more
  statements enclosed in curly brackets and
• Every statement must end with a semicolon
• A program is a series of statements
• Statements are executed in order until we run
  out of statements. But
• You can skip statements with if statements
• You can repeat statements with loops
• You can block groups of statements with and
  This is useful for if and while

9
Syntax

• Syntax just means the way a statement is put
  together.
• Computer and human languages must have correct
  syntax, and every language has its own syntax .
• You understand the dog my homework ate,
  although its syntax is wrong for English.
  (However, the syntax would be right for German
  Der Hund meine Aufgaben frass.)
• Computers never understand incorrect syntax!

10
A C Program
main() // a // is a comment int x 3
// x is a variable int y, z // y z are
variables x x 2 // assignment
statement if (x lt 6) // if statement y
2 // more assignment statements z 5
11
Variables

• How does a computer get a program?
• You load it into memory
• You store programs and information (data) in
  memory. You dont (usually) need to know where
  the program is in memory the computer knows
  where to look.
• For example, your program might start at memory
  locations (the addresses of bytes of memory) 100
  to 200 and your data at memory addresses 201 to
  275.
• Its difficult for humans to deal with numbered
  memory addresses, so you can name them. Named
  addresses are called variables.
• You must declare (name) a variable before you
  can use it.
• int x names a variable x. Where is it in memory?
  Who cares you can just call it x.

12
Assignment

• How do you put values into a variable? With an
  assignment statement.
• x 3 // put a 3 in variable x
• The sign means put whatever is on the right
  side into the left side. The right side value is
  not changed.
• The right hand side of the can be an
  expression.
• x y 3 48

13
IF statement
Sometimes you want to do something only in
certain conditions, so you can use an if
statement. If the expression inside the
parentheses is true, then you do the statements
between the and otherwise you skip
them. if (motor_speed gt 255) motor_speed
255
14

• In the line-following example, you were
  introduced to if statements
• The elementary form is if (condition)
• statements
• The statements are performed if condition is
  true, otherwise the statements between and
  are skipped.

15

• Defining philosophical truth is difficult C
• programming, however, truth is easy to define.
• A condition is true if it evaluates to non-zero.
• A condition is false if it evaluates to zero
• This can take a little getting used to, but
• basically all C expressions must evaluate
• to a number

16

• Lets look at some conditions
• if (1)
• if (-1)
• if (0)
• if (x gt 3)
• if ((x lt 3 v r lt 1) 1)
• Because expressions evaluate to a number, you can
  (but shouldnt) do some weird things
• j h gt q // if h gt q then assign 1 to j, else
  assign 0
• x !x // if x ? 0 assign 0 to x, else assign 1
• x !(!x)

17

• Looking at the line-follower code, each of the 3
  if statements can be true or false and may be
  executed in any combination

18

• But if you want to test for exclusive conditions,
  use else clauses if (condition 1) // Order is
  important for logic and efficiency
• ...
• else if (condition 2)
• else if (condition 47)
• else
• // come here when all the other conditions are
  false

19
Switch Statement

• If you have many conditions, consider using a
  switch (case) construct define FORWARD 483
  switch (condition)
• case 1 // must be number or constant expression
• break // if you leave out break, the next case
  executed BAD!
• case FORWARD
• break
• default

20
Training Days

• Mondays Engineering
• Wednesday Electrical
• Thursdays Media
• - We will also be working on the robot to
  prepare for CAL games on Thursday This is an
  open build meeting - all members are encouraged
  to come and work with veteran members to prepare
  for competitions we will let you know each week
  if we are meeting on Thursday This week we are
  not.
• Fridays Mechanical