The Simple if Structure¶

if "relation"
    "statement"
end

G = 10;
if G<50
    disp('G is a small value equal to:')
    disp(G);
end

G is a small value equal to:
    10

The if/else Structure¶

if "relation"
    "statement1"
else
    "statement2"
end

A = [1 3 6; 2 8 4];
B = [2 1 0; 3 7 1];
if size(A,2) == size(B,1)
    result = A*B
else
    disp('The number of columns of the first matrix must equal the number of rows of the second matrix')
end

The number of columns of the first matrix must equal the number of rows of the second matrix

x = input('Enter a value of x greater than 0: ');

Enter a value of x greater than 0: 4

if x>0
    y = log(x)
else
    beep
    disp('The input to the log function must be positive')
end

y = 

    1.3863

The if/else Structure¶

if "relation1"
    "statement1"
elseif "relation2"
    "statement2"
else
    "statement3"
end

age = 17;
if age<16
    disp('Sorry - you will have to wait')
elseif age<18
    disp('You may have a youth license')
elseif age<70
    disp('You may have a standard license')
else
    disp('Drivers over 70 require a special license')
end

You may have a youth license

Switch and Case¶

switch "variable"
case "option1"
    "code to be executed if variable is equal to option 1"
case "option2"
    "code to be executed if variable is equal to option 2"
.
.
.
case "optionN"
    "code to be executed if variable is equal to option N"
end

city = input('Enter the name of a city in single quotes: ');

Enter the name of a city in single quotes: 'Boston'

switch city
case 'Boston'
    disp('$345')
case 'Denver'
    disp('$150')
case 'Honolulu'
    disp ('Stay home and study')
otherwise
disp('Not on file')
end

$345

menu('mtitle','option1','option2',. . .,'optionN'): Creates a multiple-choice dialog box

city = menu('Select a city from the menu: ', 'Boston','Denver','Honolulu');

If you choose "Denver".

switch city
case 1
    disp('$345')
case 2
    disp('$150')
case 3
    disp('Stay home and study')
otherwise
    disp('Not on file')
end

$150

For Loops¶

for "index = [matrix]"
    "commands to be executed"
end

for k = [1,3,7]
    k
end

k =

     1


k =

     3


k =

     7

for x = 1:3
    a = exp(x)*2
end

a =

    5.4366


a =

   14.7781


a =

   40.1711

for k = 1:5
    a(k) = k^2
end

a =

     1


a =

     1     4


a =

     1     4     9


a =

     1     4     9    16


a =

     1     4     9    16    25

scores = [76, 45, 98, 97, 93];
count = 0;
for k = 1:length(scores)
    if scores (k) > 90
        count = count + 1
    end
end

count =

     1


count =

     2


count =

     3

While Loops¶

while "criterion"
    "commands to be executed"
end

k = 0;
while k < 3
    k = k + 1
end

k =

     1


k =

     2


k =

     3

k = 0;
while k < 3
    k = k + 1;
    b(k) = 5^k
end

a = 2;
while a < 12
    a = a + 3
end

a =

     5


a =

     8


a =

    11


a =

    14

scores = [76, 45, 98, 97];
count = 0;
k = 0;
while k < length(scores)
    k = k+1;
    if scores(k) > 90
        count = count + 1
    end
end

x = input('Enter a positive value of x ')
while x <= 0
    disp('log(x) is not defined for negative numbers')
    x = input('Enter a positive value of x ')
end
y = log10(x);
fprintf('The log base 10 of %4.2f is %5.2f nn', x, y)

Enter a positive value of x -2

x =

    -2

log(x) is not defined for negative numbers

Enter a positive value of x 2

x =

    2

The log base 10 of 2.00 is 0.30

Nested Loops¶

x = [1 2 6 3; 4 8 2 1; 12 18 3 5; 6 4 2 13];
[rows, cols] = size(x);
for k = 1:cols
    maximum(k) = x(1,k);
        for j = 1:rows
            if x(j,k) > maximum(k)
                maximum(k) = x(j,k);
            end
        end
end

maximum

maximum =

    12    18     6    13

Break¶

break: Terminates execution of a for or while loop.

n= 0;
while n<10
    n = n + 1;
    a = input('Enter a value greater than 0: ')
    if a<=0
        disp('You must enter a positive number')
        disp('This program will terminate')
        break
    end
    disp('The natural logarithm of that number is ')
    disp(log(a))
end

Enter a value greater than 0: -3

a =

    -3

You must enter a positive number
This program will terminate

n= 0;
while n<10
    n = n + 1;
    a = input('Enter a value greater than 0: ')
    if a<=0
        disp('You must enter a positive number')
        disp('This program will terminate')
        break
    end
    disp('The natural logarithm of that number is ')
    disp(log(a))
end

Enter a value greater than 0: 2

a =

    2

The natural logarithm of that number is
    0.6931

Enter a value greater than 0:

Tip: In order to break a loop in the command window you can use ctrl+C.

Continue¶

continue: Passes control to the next iteration of a for or while loop.

n = 0;
while n<10
    n = n + 1;
    a = input('Enter a value greater than 0: ')
    if a <= 0
        disp('You must enter a positive number')
        disp('Try again')
        continue
    end
    disp('The natural logarithm of that number is ')
    disp(log(a))
end

Enter a value greater than 0: -3

a =

    -3

You must enter a positive number
Try again
Enter a value greater than 0: 2

a =

    2

The natural logarithm of that number is
    0.6931

Enter a value greater than 0: 4

a =

    4

The natural logarithm of that number is
    1.3863

Enter a value greater than 0:

Recall: Relational and Logical Operators¶


<	less than
<=	less than or equal to
>	greater than
>=	greater than or equal to
==	equal to
~=	not equal to
&	and
~	not
$\mid$	or
xor	exclusive or