The code below is Pseudocode.
Sequence
Sequence is each statement after another.
x = 0
OUTPUT ("Hello world")
are examples.
Selection
When a decision needs to be made we use a selection. There are three.
One-way (if then)
IF x > 1
OUTPUT ("x is greater than 1")
END IF
Two-way (if then else)
IF (x > 1) THEN
OUTPUT ("x is greater than 1")
ELSE
OUTPUT ("x is not greater than 1")
END IF
Multi-way (case, nested if)
CASE x OF
> 1 : OUTPUT ("x is greater than 1")
== 1 : OUTPUT ("x equals 1")
< 1 : OUTPUT ("x is less than 1")
END CASE
or
IF x > 1 THEN
OUTPUT ("x is greater than 1")
ELSE
IF x == 1 THEN
OUTPUT ("x equals 1")
ELSE
OUTPUT ("x is less than 1")
END IF
END IF
Iteration
When you need to repeat something in code we use iteration. There are two types of iteration.
Pre test (while)
x = 10
WHILE x > 0 DO
OUTPUT ("x equals ", x)
x = x - 1
END WHILE
Pre test (for)
FOR x = 10 to 0
OUTPUT ("Counting down x ", x)
END FOR
Post test
x = 10
REPEAT
OUTPUT ("x equals ", x)
x--
UNTIL x <= 0
Note: There is no post test loop in Python.
Note the use of x–, this decreases the variable x by 1, it is shorthand for x = x – 1. x++ would increase the variable x by 1.