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Atatürk University
Control Statements
Atatürk University
Prof. Dr. İrfan KAYMAZ
Computer Programming in
MATLAB
Atatürk University Engineering Faculty
Department of Mechanical Engineering
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Control Statements
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Control statements: Conditional statements: if, else, elseif, switch
Repetition statements: while, for
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Control Statements
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You can also use disp command to display a message enclosed in apostrophes (called a string), or to display an array
‘disp’ command
To display a message and a value on the same line, use the following trick:
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Control Statements Example 1
Write a Matlab program taking the numerator and denominator from the keyboard, and writing «please enter a number other than zero» message if user enters zero to denominator, and then computing the ratio of them.
clear
N = input(‘enter numerator: ');
D = input(‘enter denominator: ');
if D==0
Disp(‘please enter a number other than zero‘)
else
ratio= N/D
end
Note that if user enters zero as denominator for a second time, D will be zero, and Matlab produces an error.
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Control Statements Example 2
Write a Matlab program taking the month number from keyborad and then displaying the day number of that month.
Footnote: if user enter a number other than the numbers from 1 to 12, the program will display «it takes 30 days» message. Please change it to display «please enter a number from 1 to 12» message.
clear
m= input(‘which month's day number would you like to learn (1-12)= ' );
if m==1 | m==3 | m ==5 | m==7 | m==8 | m==10 | m==12
disp(‘it takes 31 days‘)
elseif m==2
disp(' it takes 28 days‘)
else
disp(' it takes 30 days‘)
end
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Control Statements Example 3
Write a Matlab program that asks the user for a mid-term and final grade for a student and then determining the letter grade to the following scheme:
Condition Letter grade
--------- ------------
mean >= 90 A
75 <= mean < 90 B
60 <= mean < 75 C
45 <= mean < 60 D
others F
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Control Statements
switch conditional statement can be used to construct a program that takes different actions depending on the value of an expression. Switch command changes the tasks among several cases, based on expression.
Control Statements
Conditional statements: if-end, switch-end
switch expression
case {expression1}
statements
case {expression1}
statements
.
.
otherwise ►optional
end
brace or curly paranthesis
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Control Statements Example 4
Write a Matlab program asking any number from 1 to 10 and then displaying whether the number is an even or odd.
num=input(‘enter a number from 1 to 10 :’);
switch num
case {1,3,5,7,9}
disp(‘that is an odd number’)
case {2,4,6,8,10}
disp(‘that is an even number’)
otherwise
disp(‘that is not between 1-10’)
end
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Control Statements Example 5
Write another Matlab program for the month example by using the switch command.
clc
clear all
m = input(which month's day number would you like to learn (1-12)= ');
switch m
case {1,3,5,7,8,10,12};
disp(' it takes 31 days ')
case {2}
disp(' it takes 28 days ')
case {4,6,8,9,11};
disp(' it takes 30 days ')
end
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Control Statements
A loop is a structure that allows a group of commands to be repeated.
In many of programming applications, it is necessary to perform a procedure again and again. To perform this type of statements, a type of loop can be used.
In a loop structure, the program asks a question, and if the answer requires an action, it is performed and the original question is asked again until the answer is such that the action is no longer required.
Control Statements
Repetition statements (LOOPS): for-end, while-end
You can use for loop If you want to execute the statements for a
fixed, predetermined number of times.
You can use while loop If you want to execute the statements for an
undetermined number of times. A while loop repeats a group of
commands as long as a specified condition is true.
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Control Statements for-end
SYNTAX
for variable= initaial value : end value
statement
statement
…..
end
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Control Statements Example 6
Write a Matlab program that computes the sum of the numbers from 1 to 20
clear
toplam = 0 ;
for x = 1:20
toplam = toplam + x ;
end
toplam
In algebra, x =x +1 is not a true statement, but in computer programming, it is used to replace the value in memory location named x with a new value equal to x+1.
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Control Statements
clear
sayi=input(‘Enter a number=‘)
toplam=0 ;
carpim=1 ;
for i=1:sayi
toplam=toplam+i ;
carpim=carpim*i ;
end
toplam
carpim
Example 7
Write a Matlab program that computes the sum and product of the numbers from 1 to a number esked from user by keyboard.
- Be sure to supress intermediate calculations.
- Use ‘ctrl c’ to stop the calculation.
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Control Statements fprintf
To control exactly what your output looks like, you should use the fprintf function.
The fprintf statement is much more flexible (and therefore more complicated!) than disp.
General form of fprintf command:
fprintf (‘text %g \n’, variable)
Text : text to be displayed
%g : Format specifier
\n : new line (skip to beginning of next line)
variables: a comma-separated list of variables to be displayed according to the location of format specifiers in the text
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Control Statements fprintf
Some of other format specifiers
%d or %i : Base 10 values
%e : exponential notation
%f : fixed point notation
%c : single character
%s : string of characters
>> T=100;
>> fprintf('The temperature is %g °C \n', T)
The temperature is 100 °C
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Control Statements Example 8
Write a Matlab program that displays the following table
Number Team
---------------------
1. Fenerbahçe
2. Fenerbahçe
3. Fenerbahçe
4. Fenerbahçe
5. Fenerbahçe
fprintf(NUMBER TEAM\n')
fprintf('-------------------\n')
for i=1:5
fprintf('%g. Fenerbahçe\n',i)
end
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Control Statements Example 9
Write a Matlab program that displays the numbers from 1 to 10 and squares of
them in two column.
Before writing the program, examine the followings.
balance = 12345;
rate = 0.09;
interest = rate * balance;
balance = balance + interest;
fprintf( 'Interest rate: %g New balance:%g\n',rate, balance )
Interest rate: 0.09 New balance:13456
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Control Statements Homework 1:
In a cargo company, a pricing policy according to the package weight is as follows;
Base price is 5 TL for packages up to 2 kg. For the packages heavier than 2 kg, 0.5 TL should be added to the base price for every 1 kg. If the packages is heavier than 35 kg, 10 TL should be added to the total price. The packages heavier than 50 kg are not accepted because of worker’s health. Write a Matlab program that computes the price according to the above-mentioned scheme and then prints the following table for 1:50 kg pacages.
(Assume that the scale readings are only integer values)
Weight (kg) Price (TL)
1 5
2 5
3 5.5
4 6
… …
50 39
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Control Statements while-end
A while loop repeats a group of commands as long as a specified condition is true.
Syntax:
while expression
statements
…
end
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Control Statements Example 10
Write a Matlab program that computes the summation of the number from 5 to 10.
a=4;
T=0
while a<10
a=a+1;
T=T+a;
end
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Control Statements Example 11
Write a Matlab program that prints your name 10 times.
a=0 while a<10 a=a+1; disp('MATLAB') end
Don’t forget that you can stop the calculation with ‘ctrl c’
If you write an infinite loop into a program and want to stop it,
use ctrl-c.
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Control Statements Example 12
Write a Matlab program that computes the root of the following equation (first degree) according to the flowchart. A and B coefficients must be entered from keyboard. If user enters zero as A (as long as A is zero), entering must be repeated. Ax+B=0
A=input('input A : '); while A==0 A=input('input A : '); end B=input('input B : '); x=-B/A; fprintf(' root = %g \n',x)
= e
h
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Control Statements Example 13
Let a=10 and b=7. Write a Matlab program that computes the number of repetition to reach the summation of a and b to 100000 level by increasing a and b two times for each repetition.
a=10;b=7;counter=0; t=0; while t<100000 counter=counter+1; a=2*a; b=2*b; t=a+b; end fprintf('%g \n',counter)
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Control Statements break
break command terminates the execution of a for or while loop.
Statements in the loop that appear after the break statement is not executed.
for j=2:6 if j==4 break end end fprintf(‘j= %g \n”, j) disp(‘loop ended’)
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Control Statements Example 14
Nested for loops: for loops can be nested inside each other.
clc
clear
t=0;
for i = 1:5
t = 0;
for j = 1:5
t = t + j;
end
c = t * i;
end
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Control Statements Example 15
Write a MATLAB program that prints the multiplication table.
for a=1:10
for b=1:10
c=a*b;
fprintf(‘%g * %g = %g\n’, a, b, c)
end
end
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Control Statements mod
mod(X,0) ----- X
mod(X,X) ----- 0
mod(X,Y) ----- if x<y, x
if x>y, remainder of x/y division
mod(3,0)
ans =
3
