Flowcharts and pseudocode

An algorithm can be shown in two ways: as a flowchart (a picture) or as pseudocode (text). Both show the logic and the flow of control, not the details of any particular programming language.

A flowchart uses standard symbols (Table 4.1):

• Oval: start or end (the terminator).
• Rectangle: a process (an action, such as a calculation).
• Diamond: a decision (a question with yes/no answers).
• Parallelogram: input or output of data.
• Arrow: the order in which the steps are followed.

For example, to find the cube of a number: Step 1, input num (parallelogram); Step 2, cube = num × num × num (rectangle); Step 3, print cube (parallelogram); all between a Start and an End oval.

Pseudocode means 'not real code'. It describes the steps in plain, informal language for people to read; a computer cannot execute it. Common keywords: INPUT, COMPUTE, PRINT, INCREMENT, DECREMENT, IF/ELSE, WHILE, TRUE/FALSE.

Pseudocode helps programmers not to miss any step, and lets people who do not program review the logic. An example, to find the area and perimeter of a square:

• INPUT side
• COMPUTE Area = side * side
• COMPUTE Perimeter = 4 * side
• PRINT Area, Perimeter