Matlab tutorial 3

MATLAB TUTORIAL 3
By Norhan Abdalla

Outline:
■ Input /Output Control
■ Logical Structures
■ Repetition Structures

User Defined Input
■ This is mainly when the
program deals with a person
other than the programmer.
■ Using the command ‘input’:
▪ It can be a scalar
▪ It can be a matrix
▪ It can be a string:
• Having this ‘s’ as a parameter , means
that you don’t have to insert the string
in a single quotation

Output
■ Using the command ‘disp()’
■ If you want to include the apostrophe , you have to use it twice unless
MATLAB will interpret it as terminating the string.

Try this:
■ You can use a combination of the ‘input’ and ‘disp’
functions to mimic a conversation.
Try this using
an M-file

Formatted Output
■ fprintf A function controls the output and adjust its
format.
• General form:
fprintf( format setting , variable….)
• % is a place holder for the variable and the variable is
specified later.
You can’t hold
a place by just
using ‘%’, a
formatting style
must be used

Formatting the Output
■ To insert new line , use (‘n’)
Type
Field
Result
%f Fixed-point notation
%e Exponential notation
%d Decimal notation( doesn’t include trailing
zeros
%g Whichever is shorter , %f or %e
%c Character information( one character at a
time
%s String of characters( the entire string)
Format
command
Result
n linefeed
r Carriage return
t Tab
b backspace

Formatting the Output
■ Adjusting the precision :
■ If a variable is a two dimensional matrix , MATLAB uses the values one
column at a time.
■ Try this , What do you notice?
8.4 reserves a place
for 8 digits 4 of them
are decimals

Formatting Output
■ To output in a file , you first have to create a file
,open an output file and assign an identifier to it.
■ If you want to include a ‘%’ in an fprintf function ,
you must use it twice unless MATLAB will interpret
it as a place holder.
identifier Function that opens a
file
File’s name Write data to the file
The output in the file

Relation & Logical Operators
■ MATLAB uses number 1 for true and 0
for false ( actually it takes any non zero
number as true)
■ Notice the difference between ==(equal operator) and
= (assignment operator).
Relational
Operator
Interpretation
< Less than
<= Less than or equal
> Greater than
>= Greater than or equal to
== Equal to
~= Not equal to

Relation & Logical Operators
Logical
Operator
Interpretation
& And
~ Not
| Or
xor Exclusive or
&& And (with scalars)
|| Or (with scalars)
■ The difference between & and
&& is that && is used for
scalar quantities only.
■ & is used for expressions.

Logical Functions
Find
■ find Searches a matrix and
identifies which element in that
matrix meets a given condition.
■ Try this:
Indexes
Elements
Try this using
an M-file

Practice:
𝑥 =
1 10 42
5 8 78
56 45 9
6
23
13
y =
1 2 3
4 10 12
7 21 27
z = 10 22 5 13
23 22 8 9
• Find the elements in each matrix that are greater than 10.
• Find the row and column numbers for elements in each matrix that contains
values greater than 10 and less than 40.
• Find the values in each matrix that are greater than 10 and less than 40.
• Use the length command together with results from the find command to
determine how many values in each matrix are between 0 and 10 or
between 70 and 80.
• Define the following matrices:

Selection Structures
■ The general form :
if comparison
{ statements }
end

■ This structure allows us to execute a series of
statements if the condition is true , and skip
those steps if the condition is false.
■ If x is a matrix ( x = 0:0.5:2;) , ‘if’ statement is
true only ,if it is true for every element in the
matrix.
• Hint :
MATLAB includes a function called ‘beep’ that causes the
computer to “beep” at the user.

■ This structure allows us to check multiple criteria while
keeping the code easy to read.
■ Remember that : if age is a matrix , every condition is true for
all the elements evaluates to true.
Try to change
age and notice
the result

Practice:
■ Try this:
■ Grading Marks:
• Prompt the user to enter the mark
• Check the mark based on the mark table
• Display the mark
Mark Grade
90 to 100 A
80 to 90 B
70 to 80 C
60 to 70 D
Less than 60 F

Switch
■ This structure allows you to choose between multiple
outcomes , based on some criteria.
■ General form:
Switch variable
case option1
code for option 1 if true
case option2
code for option 2 if true
otherwise
code to be executed if non of the cases were true
end

Basic Parts for a Loop
■ Parameter used to terminate the loop.
■ Initialization of the parameter.
■ Process that changes the parameter at each iteration.
( unless it becomes unstoppable )
■ Comparison –using the parameter –to a certain condition to
decide when to end the loop.
■ Calculation inside the loop
Initialize a
parameter
Condition
for the
loop
start
calculation

Types of Loops
■ For loop  When you know how many times of
operations’ iterations to repeat the loop.
■ While loop  It repeats the instructions till a certain
condition is met.
■ Midpoint break loop It is useful for situations where the
commands in the loop must be executed at least once ,till
some condition is met.
Remember in
C++ the do-while
loop?

For Loop:
■ General form:
for index = [ matrix]
commands to be executed
end
■ If k (the index) is a matrix,
MATLAB uses an entire column as
the index each time through the
loop.
■ Hint : once you have completed the
for loop , the index k retains the
last value used.
• For example if the loop repeated 5 times
, after breaking out of it k will be 5
K is a matrix ,
but at each
iteration ,it
takes one value
only.
New element is
added to the
matrix each
time

Practice:
■ A list of test scores , count the number of students above 90.
Ex :
■ Calculate the factorial with a for loop.
■ Use a counter to find how many values greater than 30 , x = [ 45,23,17,34,85,33].
■ Repeat the above exercise with the find command.
■ Use a for loop to sum the elements of x , check your result with the sum function.

While Loop:
■ General form:
while condition
commands to be executed
end
■ Hint :
• The variable used to control the
while loop must be updated every
time through the loop. If not,
you‘ll generate an infinite loop.
• In case of instructions that may
take a lot of time to be executed,
you can always exit the
calculation of a loop manually ,
type ctrl+c

Practice:
■ Consider x = [ 43 ,29 , 16 , 32, 85, 37] , use a while loop to
count how many values that are greater than 35.
■ Use a while to sum the elements in x.
■ Use a while loop to create a vector containing 10 elements
as shown:
Τ
1
1 , Τ
1
2 , Τ
1
3 , Τ
1
4 ……….. Τ
1
10
■ Use a while loop to create a vector containing 10 elements
as shown:
Τ
1
1 , Τ
−1
2 , Τ
1
3 , Τ
−1
4 ……….. Τ
−1
10

Break and Continue:
■ break  Used to terminate a
loop permanently even if the
comparison is still true.
■ continue  Used to ignore the
current iteration and continues
with the loop.

Midpoint Break Loop:
■ In this structure , the loop is
entered , calculations are
processed , and a decision is
made at some arbitrary point to
exit the loop.
■ The loop must be executed at
least once.
1 indicates
true, while
the
condition is
always true
The loop is
executed once
Or it will keep running until the
condition of num_candy <0 is false
You break
from a mid
point in the
loop

Nested Loops:
■ Examine the following
example:
• A loop for finding the sum of
every column in a matrix.
■ Hint :
• To know how much time your
calculations take to be
complete you can you the
command :
tic – toc
tic  before
the instructions
toc  after the
instructions

Matlab tutorial 3

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