MATLAB Programming - Loop Control Part 2

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1

INTRODUCTION
In this lecture we will discuss more
about Loop control.
- Switch – case commands
- Nested lops
- break command
- continue command
2
e l e c t r i c a l e n g g t u t o r i a l . b l o g s p o t . c o m

SWITCH - CASE
• There is no conditional statement.
• It choose code to execute based on
value of scalar or string, not just
true/false
• Different codes can be executed
based on the value of the scalar.
• It is easier than if-elseif-end
commands if the conditions are more.
3

SWITCH-CASE SYNTAX
4

SWITCH-CASE SYNTAX…
• The expression after switch command is
evaluated first.
• If the obtained value is equal to
value1 – then commands below case value1
is executed up to
next case or otherwise or
or end statement.
• Similarly if the obtained value is equal
to value2 – then then commands below case
value2 is executed.
• If switch-expression not equal to any of
the values in case statement, commands
after otherwise executed.
• If otherwise command is not present, no
commands are executed
5

SWITCH-CASE EXAMPLE
id = input(‘enter your id’)
switch id
case ‘321456'
display (‘You name is Martin’)
case ‘320423'
display (‘You name is Allen’)
case ‘332458'
display (‘You name is Mohan’)
case ‘321564'
display (‘You name is Vicky’)
otherwise
display (‘You are not a member of the
class’)
end
6

NESTED LOOP
• A loop or conditional statement is
placed inside another loop or
conditional statement.
• Simply, a loop within a loop
• Both for and while loops can be
nested.
7

NESTED LOOP SYNTAX
for ii = 1:n
for jj = 1:m
<Commands>
end
end
while expression1
while expression2
< Commands >
end
end
8

NESTED LOOP EXAMPLE
Program to display a 2D matrix
M = [1 2 3; 4 5 6; 7 8 9];
[r c] = size(M);
for Row = 1:r
for Col = 1:c
fprintf('Element(%d,%d)= %d.n',
Row, Col, M(Row, Col))
end
end
9

NESTED LOOP EXAMPLE…
I=1; N=10;
while I<=N
J=1;
while J<=N
A(I,J)=1/(I+J-1);
J=J+1;
end
I=I+1;
end
10

BREAK COMMAND
• When inside a loop (for and
while), break terminates
execution of loop
• MATLAB jumps from break to end
command of loop, then continues
with next command (does not go
back to the for or while command
of that loop).
• ‘break’ ends whole loop, not just
last pass
• If break inside nested loop, only
nested loop terminated (not any
outer loops)
• break command in script or
function file but not in a loop
terminates execution of file
11

BREAK EXAMPLE
Program to display prime numbers from 1 to
50. The program exit from the inner loop
using break, if the number is not a prime.
for n=2:50
for m=2:50
if(~mod(n,m))
break
end
end
if(m > (n/m))
fprintf('%d is primen', n); end
end
12

CONTINUE COMMAND
• Used to stop current iteration
and start next iteration in a
loop
• Can be used with both for- and
while loops
• ‘continue’ is used usually as
part of a conditional
statement.
• When the program execution
reaches ‘continue’ it stop
executing the remaining
commands in loop and jump to
the end command of loop and
then starts a new iteration
13

CONTINUE EXAMPLE
a = 1;
while a < 20
if a == 15
a = a + 1;
continue; % skip the iteration for a=15
end
fprintf('value of a: %dn', a);
a = a + 1;
end
14

MATLAB Programming - Loop Control Part 2

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