Structured Programming
and Applications
A. Haghighat M.
Department of Building, Civil & Environmental Engineering
(BCEE 231)
Lecture 1 (January 13, 2025)
Today’s lecture:
- An overview of Structured Programming
- Advantages of Matlab Programming
- Vectors and Matrices in Matlab
Textbook: Chapters 1 & 2
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Motivation for Structured Programming
• The computer programs used in engineering applications are written using high-level
languages because of their clarity.
• These languages have to follow strict logical statements which will be our focus in
this course.
• Structured programming aims at improving clarity, (logical) quality, and development
time of a computer program.
• Common features of structured programs are their modularity and use of block
procedures such as subroutines and functions, as well as control statements for the
logical flow control; these features make the use of structured programming suitable
for scientific and engineering applications.
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Elements of Structured Programming – Control Structures
Sequence: Simply doing one instruction (task) then the next and the next. Just do them in
a given sequence or in the order listed.
Example: Baking bread requires the execution of a list of statement in a sequence.
Add flour to bowl → Add salt → Add yeast → Mix → Add water → Knead → Let rise → Bake
Iteration: The code or algorithm is executed for a certain number of times Or might not be
executed at all (repeats zero time) Or executed indefinitely until some conditions are met.
Example: Washing dishes requires iterations.
Stack dishes
by sink
Fill sink with hot
soapy water
Get dish from
counter
Selection: This is where you select or
choose between two or more flows. The
choice is decided by asking some sort of
question/condition.
The
answer
then
determines the path (or which lines of the
code) will be executed.
Wash the
dish
Put dish in
drain rack
Wipe off
counter
Rinse out
sink
Example: Sorting mail requires selection.
Read it
If personal
If magazine
Get mail from
mailbox
If bill
If ads
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Magazines basket
Pay it
Put in recyclables bin
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Elements of Structured Programming – Operators
Arithmetic operators: Give us results for certain mathematical operations.
Relational operators: Check whether an expression is True or False
Example:
Structured Programming and Applications
2 == 3
False
2 \= 3
True
2>3
False
2<3
True
2 >= 3
False
2 <= 3
True
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Elements of Structured Programming – Operators
Logical operators: Are both statements True? Is either statement True?
Example:
AND
True only if both statements are True
OR
True if either item is True
3 + 5 > 6 AND 18 < 21
True AND True
True
3 + 5 > 10 AND 18 < 21
False AND True
False
3 + 5 > 10 AND 18 < 18
False AND False
False
3 + 5 > 6 OR 18 == 18
True OR True
True
3 + 5 > 6 OR 18 == 21
True OR False
True
3 + 5 > 16 OR 18 == 21
False OR False
False
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Elements of Structured Programming – Variables and Arrays
Variable: Variable is an area of memory that stores one item of data. Variables basically serve
two purposes:
1. The programmer can choose the names of the variables, making coding easier.
2. Programs or functions can be developed using variables in a way that they work with any values.
Types of variables
Integer
Integers are whole numbers; integer variables are used when we are certain
there not going to be any need for numbers after the decimal point. e.g., if you
are counting people, cars, etc.
Real or float
Numbers that contain fractional parts or in other words numbers with a decimal
place (e.g., 2.2).
Character
A character variable stores either a single letter (e.g., ‘s’) or multiple letters (e.g.,
‘storm’).
Boolean
A Boolean variable can store on of the two values – either TRUE or FALSE
Array: An array is the most fundamental representation of information and data. Arrays are
a collection of several values of the same type.
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Elements of Structured Programming – Functions
Functions
• Within a computer program, a function is a sequence of program instructions that
performs a specific task, packaged together.
• Function is a block of organized, reusable code that can be used within a program
wherever that particular task should be performed.
• Functions provide better modularity for your application and a high degree of code
reusing. Variables are passed to a function by value.
• Functions can be used within command lines like variables.
• Functions help reducing code size, and improve readability and debugging procedure
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Choosing a programming language, Why MATLAB?
• Be easy for beginners to learn, understand, and implement
• Be a general-purpose programming language
• Be interactive
• Shield the user from detail understanding of the computer hardware and operating
system
• It is high-level programming language which allows quick coding
• Use of arrays is very flexible.
• Many built-in functions and toolboxes are available.
• Easy to use visualization tools (e.g., graphs, charts, etc.) are offered in MATLAB.
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MATLAB Environment
• The simplest method for using MATLAB is interactively; an expression is entered by the
user and MATLAB responds immediately with a result.
prompt
Command window
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MATLAB Environment
• In command window, user and MATLAB can communicate in real time; e.g., MATLAB
can be your calculator. You can enter any expression or command at the prompt.
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MATLAB Environment
• Some commands that allow you to get help from MATLAB: demo, help, lookfor, doc
➢ To exit from MATLAB, either type quit or exit at the prompt, or click on “x”.
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Variables in MATLAB
To store a value in a MATLAB session, or in a program, a variable is used. The Workspace
Window shows variables that have been created and their values.
An easy way to create a variable is to use an assignment statement: variablename = expression
meaning: “variable b gets the value of 3,
not “variable “b” equals 3”
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Variables in MATLAB
• Note that the variable name must always be on the left, and the expression on the right. An
error will occur if these are reversed.
• You can use a semicolon at the end of a statement to suppress the output from being printed
out.
• A shortcut for retyping commands is to hit the up arrow ↑, which will go back to the
previously typed command(s). This is very useful, especially if a long expression is entered
and it contains an error, and it is desired to go back to correct it.
• To change a variable, another assignment statement can be used, which assigns the value
of a different expression to it.
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Variables in MATLAB
Variable Names
❑ The name must begin with a letter of the alphabet. After that, the name can contain letters,
digits, and the underscore character (e.g., value_1), but it cannot have a space.
❑ There is a limit to the length of the name (it is 63); the built-in function namelengthmax
tells what this maximum length is.
❑ MATLAB is case-sensitive, which means that there is a difference between upper- and
lowercase letters. So, variables called mynum, MYNUM, and Mynum are all different.
❑ There are certain words called reserved words, or keywords, that cannot be used as
variable names (e.g., for, if, float, return, while, continue, etc.)
❑ Names of built-in functions (eye, rectangle, sin(), etc.) can but should not be used as
variable names.
❑ Some useful functions for working with variables: who, whos, clearvars, clear
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Variables in MATLAB
• In the Workspace Window, the variable name, value, and class (which is essentially its type)
can be seen.
• The function class can be used to see the type of any variable:
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Numerical expressions in MATLAB
❖ The default in MATLAB is to display numbers that have decimal points with four decimal
places. The format (short or long) command can be used to specify the output format of
expressions.
❖ Continuation operator (ellipsis): Especially long expressions can be continued on the next
line by typing three periods.
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Numerical expressions in MATLAB
Operators
+
addition
Negation or subtraction
*
multiplication
/
division (divided by e.g., 10/5 is 2)
\
division (divided into e.g., 5\10 is 2)
^
exponentiation (e.g., 5^2 is 25)
Operator Precedence Rules (PEMDAS)
()
parentheses
^
exponentiation
negation
*, /, \
all multiplication and division
+, addition and subtraction
* Within a given precedence level, the
expressions are evaluated from left to right
Constants
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Numerical expressions in MATLAB
Built-in functions
To call a function, the name of the function is given followed by the argument(s) that are
passed to the function in parentheses.
❑ Some of the other built-in functions: fix, floor, ceil, mod, exp, log, and log10
* To see a list of elementary math functions, >> help elfun
generates one random real number in the open interval (0,1)
generates random real numbers
returns a random integer in the range (inclusively)
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Characters and strings in MATLAB
➢ A character in MATLAB is represented using single quotes (e.g., ‘a’ or ‘x’).
➢ Characters are put in an order using what is called a character encoding.
➢ In the character encoding, all characters in the computer’s character set are placed in a
sequence and given equivalent integer values.
➢ Standard ASCII has 128 characters, which have equivalent integer values from 0 to 127.
➢ The character set includes all letters of the alphabet, digits, and punctuation marks.
➢ Strings are sequences of characters in double quotes (e.g., "ciao").
➢ To know the integer associated with a character you can use built-in function double
➢ To know the character associated with an integer you can use built-in function char
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Relational expressions in MATLAB
Relational (Boolean) expressions
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Vectors and Matrices in MATLAB
❖ Everything in MATLAB is written to work with vectors and matrices. The following
slides will introduce vectors and matrices. Operations on vectors and matrices and builtin functions that can be used to simplify code will be reviewed.
❑ Vectors and matrices are used to store sets of values, all of which are the same type.
❑ A matrix can be visualized as a table of values. The dimensions of a matrix are r x c
(pronounced r by c), where r is the number of rows and c is the number of columns.
❑ A vector can be either a row vector or a column vector. If a vector has n elements, a row
vector have the dimensions 1 x n and a column vector have the dimensions n x 1.
❑ A scalar (one value) has the dimensions 1 x 1.
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Vectors and Matrices in MATLAB
Creating row vectors
• Put the values that you want in the vector in
square brackets, separated by either spaces or
commas.
• If the values in the vector are regularly spaced, the colon
operator can be used to iterate through these values.
• With the colon operator, a step value can also be specified
by using another colon, in the form (first:step:last).
• linspace function creates a linearly spaced vector; linspace(x,y,n)
creates a vector with n values in the inclusive range from x to y.
• Putting two vectors together by concatenating the vectors.
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Vectors and Matrices in MATLAB
Referring to and modifying elements of row vectors
• The elements in a vector are numbered sequentially; each element number is called the
index, or subscript. In MATLAB, the indices start at 1.
indices
elements
➢ Accessing a particular element:
(pronounced “newvec sub 5”)
➢ Accessing a subset (several elements) of a vector:
index vector
➢ Accessing a subset of a vector (any vector can
be used for the indices into another vector):
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Vectors and Matrices in MATLAB
➢ The value stored in a vector element can be
changed by specifying the index or subscript.
➢ By referring to an index that does not yet
exist, a vector can also be extended.
Creating column vectors
• One way to create a column vector is to explicitly
put the values in square brackets, separated by
semicolons (rather than commas or spaces):
• Any row vector created using any method can be
transposed to result in a column vector. In MATLAB,
the apostrophe (or single quote) is built-in as the
transpose operator.
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Vectors and Matrices in MATLAB
Creating Matrices
• For matrix, the values within a row are separated
by either spaces or commas, and the different
rows are separated by semicolons.
• Iterators can be used for the values in the rows
using the colon operator.
* There must always be the same number of values in each row and each column of
a matrix.
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Vectors and Matrices in MATLAB
❖ Matrices of random numbers can be created by rand and randi:
▪ If a single value n is passed to rand,
an n x n matrix will be created
▪ If two arguments are passed, they
specify the number of rows and
columns in that order.
▪ Matrices of random integers can be generated
using randi; after the range is passed, the
dimensions of the matrix are passed.
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Vectors and Matrices in MATLAB
❖ Several functions that create special matrices: zeros, ones, and eye:
Referring to and modifying matrix elements
• To refer to matrix elements, the row and then the column subscripts are given in parentheses:
This is called
subscripted indexing
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Vectors and Matrices in MATLAB
❖ An individual element or an entire row/column in a matrix can be modified by assigning
new values to them.
The exception to this rule is that
a scalar can be assigned to any
size subset of a vector or matrix
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Vectors and Matrices in MATLAB
❑ To extend a matrix, an individual element could not be added as that would mean there
would no longer be the same number of values in every row. However, an entire row or
column could be added:
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Vectors and Matrices in MATLAB
Vector and matrix dimensions
➢ The length and size functions are used to find dimensions of vectors and matrices.
For vectors:
For matrix:
➢ MATLAB also has a function numel, which returns the
total number of elements in any array (vector or matrix):
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Vectors and Matrices in MATLAB
Changing matrix dimensions
MATLAB has several built-in functions that change the dimensions or configuration of
matrices, including reshape, fliplr, flipud, flip, and rot90.
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Vectors and Matrices in MATLAB
Empty vectors
• An empty vector (a vector that stores no values) can be created
using empty square brackets:
➢ Values can then be added to an empty vector
by concatenating:
➢ Empty vectors can also be used to delete elements
(one or even a subset) from vectors:
➢ Individual elements cannot
be removed from matrices,
but entire/column can:
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Vectors and Matrices in MATLAB
Vectors and matrices as function arguments
• An entire vector/matrix can be passed as an argument to a function; function will be evaluated
on every element, meaning that the result will be the same size as the input argument.
• There are some functions (min, max, sum, prod) that are written specifically to operate on
vectors or on columns of matrices:
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Vectors and Matrices in MATLAB
Vectors and matrices as function arguments
• A matrix with dimensions r x c, the result for the min, max, sum, and prod functions will
be a 1 x c row vector, as they return the minimum, maximum, sum, or product for every
column.
• To work with rows, one method
would be to transpose the matrix:
• Another useful function that can be
used with vectors and matrices is diff:
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Vectors and Matrices in MATLAB
• There are also functions that return cumulative results; the functions cumsum and
cumprod return the cumulative sum or cumulative product, respectively
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Vectors and Matrices in MATLAB
• The cummin and cummax functions find the cumulative minima and maxima for
every column.
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