Loops

Review questions

• If A is an array, what is A(2:5,3)?
• If A is an array, what is A(2,1:4)?

Control statements

Control statements controls the flow of execution of your code. There are different types of control statements:

• Loops.
• Conditionals.
• Exception handling.
• Break statements.
• Parallel execution.

Loops

A loop control statement allows a block of code to be executed repeatedly. There are two basic forms

• "for" loop
• "while" loop

An example

        A = ones(1,5)
        for i = 1:4
            A(i) = 2*i;
        end
    

• A "for" loop starts with a "for" statement
• An assignment state after "for" specifies the range that will be iterated as well as variable to be used.
• It ends with the keyword "end"
• Many statements can be included in the block between "for" and "end"

Nested for loop

A loop can contain another loop.

        A = ones(8,8)
        for i = 1:5
            for j = 2:7
                A(i,j) = i+j;
            end
        end
    

• Each loop requires its own "end" keyword.
• Indentation usually improves readability.

Breaking statements

Execution of statements inside a loop can be interrupted or diverted.

• the "break" statement exit a loop
• the "continue" statement skips to the next iteration of the loop

Worksheet tasks

For today's exercise, complete the following tasks using "for" loops

• Create the array [1 2 3 ... 10]
• Create the two dimensional array whose i-j entry is i+j
• Create the gradient effect on this image

Can you recreat this?