Sequence, Selection and Iteration
Sequence
A sequence is just the same as an algorithm. A sequence is not written in a
specific programing language, but is always written in chronological order (this
could be numbered). There is an example of a sequence/algorithm below:
First do this
1. Find ‘number 1’ in memory
2. Add 12 to ‘number 1’
3. Divide total by 2
Next do this
4. Call the total ‘number 2’
5. Save back in the same file
Next do this
6. Close the file
7.
This means that the algorithm will be able to run on a sequential CPU. Most
normal computers use sequential CPU’s, meaning that they fetch, decode and
execute instructions one at a time. Parallel is the opposite of a sequence and
means that the CPU carries out multiple instructions at the same time.
Selection
Selection is similar to a sequence, but includes a decision. This works by creating
a decision and if it is true do this, or if it is false do this. This means there is more
variation. This means that the next instruction in the sequence depends on
whether the condition is true or false.
Condition
True
Carry on
from here
False
Carry on
from here
Selection can also be written in pseudo-code using the statements: if, then, else
and end. This pseudo-code shows how to double a number each time until it
reaches 16.
If (X > 16) Then
Print (X)
Else
X=X*2
Iteration
Iteration is a key part of computer code as it allows the code to loop. This can be
very useful as it can save a lot of lines of code. This could be used to program
someone walking in a game as instead of writing left one, right one, and left
one… you can just write it once and use a loop which will repeat the code until it
is programed to end. When using loop, always make sure you program it to end
otherwise the program will never end and won’t work.
Condition
True
While
condition
is true
False
Carry on
from here
This is a piece of code for a timer, written in small basic which shows sequence,
selection and iteration.