ENGR 1202: Introduction to Engineering Principles and Practice II 3. Adding Program Control to Scripts

1
ENGR 1202 Introduction to Engineering
Principles and Practice II3. Adding Program
Control to Scripts

• Jim Bowen
• Dept. of Civil Engineering
• UNC Charlotte
• August 28, 2001

2
Class Announcements

• Look for class announcements on the web
• 1st assignment deadline extended to 7 PM
• Help session added 5-7 PM, Smith 229
• Script added for submitting homework hw_submit

3
Todays Lecture

• Using check_script
• Strings and String Functions
• More on Expressions and Vectors
• In-class script
• Adding Interaction, Program Control
• input and disp
• Loops (for, while)
• Branching (if elseif else)
• Logical Expressions
• An example script

4
Using check_script

• Steps in grading your own script
• Write your script and save w/ .m extension (no
  blanks, no funny characters)
• Enter get_script at MATLAB command line
• Enter assignment number
• Enter MOSAIC username (must be exact)
• Select file to check
• Run script, note grade
• Example using assignment_one.m

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Strings, String functions (p. 4, 111)

• Strings are row vectors of type character
• phrase this class sucks! (1 x 17 char.
  Vector)
• Functions are available just for strings (p. 111)
• lower, upper - converts case
• strcmp - compare 2 or more strings
• sort - sorts characters based on ASCII code
• Examples script on web - show_strings.m
• phrase sort(phrase) note columns 1 2 are
  blanks
• strcmp(bowen,Bowen) ans 0
  (false)
• strcmp(bowen,lower(Bowen)) ans 1

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More on Expressions - Scalars

• Size(scalar) 1,1 ex3_0.m
• All the standard arithmetic operations are
  available for scalars
• addition
• - subtraction
• multiplication
• / division
• raise to a power

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More on Creating Vectors

• Colon notation can be used for creating vectors
• A 15 same as A 1 2 3 4 5
• B 11 0.5 12.5 same as B 11 11.5 12.0
  12.5
• All the standard arithmetic operations are also
  available for scalars applied to vectors
• addition - subtraction
• Multiplication / division
• raise to a power

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More on Expressions - Vectors

• Examples (ex3_1.m)
• A 3 1 2 3 4 5 (column vector)
• B sqrt( 2 1 2 3 4 5) (row vector, w/
  func.)
• C 200 .5 210 sin( 3/2 pi)

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More on Expressions - Vectors

• Operations may also be performed entry-wise
• Addition and subtraction are always entry-wise
• Multiplication, division, raising to power -- put
  dot in front to get it done entry-wise
• Examples (ex3_2.m)
• A 1 2 3 6 7 10 A 7 9 13
• B 1 2 3 . 1 2 10 B 1 4
  30
• C 1 2 3 . 3 C 1
  8 27

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In-class Script 3_1

• In the last 300 years the worlds human
  population has risen from 0.5 to 4.0 billion.
  This corresponds to an exponential growth rate, k
  .00693 yr-1. Assume exponential growth to
  calculate population for every year between 2000
  and 2100.
• Equation P P0 exp (k t), t time
• Assume t year-2000, P0 5.0, k 0.00693
• Solution ics3_1.m

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Making Your Programs Useful

• Congratulations! You are a computer programmer!
• Your programming toolbox is missing a few
  things
• Using the commands you know now, your programs
  will be
• Unable to interact with user (no inputs)
• Many lines long (no looping)
• Not very flexible (no branching)

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Making Your Programs Interactive

• Use input to get numbers and strings from
  screen
• x input(Enter a number )
• (x set to input value)
• Use disp to display strings and number to
  screen
• disp(x) (displays value w/o any
  text)
• disp( x ,num2str(x)) (display w/ text)
• Example ex3_3.m

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Adding Program Controls (p. 10)

• Useful programs are flexible
• Useful programs do a lot with few lines of code
• Program controls make these features possible
• Two types of program control
• Looping (for, while) p.10, p.11
• Branching (if) p.12
• Other commands available (I rarely use these)
• switch - case - otherwise,

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Programming Looping

• Loops are used to repeatedly execute commands
• Two types of loops
• Variable controlled loops (for) p.10
• Relation controlled loops (while) p.11

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The for command (ex3_4.m)

• for i 1 2 (i loop goes from 1 to 2 by 1)
• for j 1 3 (j goes from 1 to 3 by 1)
• a(i,j) i 2 / (j 2)
• disp( i,j, a(i,j),int2str(i),,,int2s
  tr(j),,,num2str(a(i,j)))
• end
• end
• Indenting is essential to avoid errors
• For block terminated with end
• Nested loops possible, looping goes in to out

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The while command (ex3_5.m)

• i 1 i is
  initialized
• while i lt 2 termination controlled by
  expression
• j 1 j is initialized
• while j lt 3
• a(i,j) i 2 / (j 2)
• disp( i,j, a(i,j),int2str(i),,,int2
  str(j),,,num2str(a(i,j)))
• j j1 j is
  incremented by 1
• end
• i i_ 1 i is
  incremented by 1
• end
• Termination, nesting, indentation same as before

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The if - else - end structure (p. 12)

• If logical expression 1 (e.g. i1 or j lt
  2 )
• execute this if logical expression 1 is true
• elseif logical expression 2 (optional)
• execute this if 1 is false and 2 is true
• else (also
  optional)
• execute this otherwise
• end (ex3_6.m)
• For every for, while, and if there must be a
  matching end

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In-class script 3.2

• Count the numbers between 10 and 55 that are
  evenly divisible by 6 (that is, rem(,6) 0)

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An example script lmad.m

• Shown last time as simulation of Monty Hall
  Problem
• Things to see in script
• Comment lines (start with )
• Variable assignments
• Logical expressions
• Display of strings using disp
• Script available on web lmad.m