Structured Programming

In a high-level, procedural language such as Pascal, Visual Basic, Python or C#, an algorithm can be implemented using just three basic structures:

• Sequence
• Selection
• Iteration

Sequence

A sequence consists of one or more statements following one after the other (all programs use sequence, you write them in a specific order).

Here is an example written in pseudocode:

hoursWorked = USERINPUT
hourlyRate = USERINPUT
totalCharge = hoursWorked * hourlyRate
OUTPUT “Total charge: ”, totalCharge

Selection

Selection is implemented using an IF…THEN…ELSE statement, it essentially makes a choice between one path or another.

Here is a pseudocode example:

IF sunIsShining THEN
   takeSunhat
ELSE
   takeUmbrella
ENDIF

The IF statement can also use ELSE IF to create more complex selection statements.

Here is a pseudocode example:

IF sunIsShining THEN
   takeSunhat
ELSE if Raining
   takeUmbrella
ELSE
   takeCoat
ENDIF

Some languages also have a CASE statement (switch case in C#). This allows you to replicate complex IF statements in a more straight forward way.

Here is a pseudocode example:

SWITCH (sun)
   CASE Shining:
      TakeSunHat
   CASE NotShining
      TakeUmbrella
END SWITCH