11.3 Structured Programming

Structured programming is a fundamental paradigm in computer science that emphasizes the use of control flow structures to create well-organized and easy-to-understand programs. It avoids the use of unstructured constructs like `GOTO` statements, which can lead to complex and difficult-to-debug code. The core building blocks of structured programming are sequence, selection (conditional statements), and iteration (loops).

Key Concepts

• Sequence: Instructions are executed in a linear order.
• Selection: Allows the program to make decisions based on conditions (e.g., `if`, `else if`, `else`).
• Iteration: Enables the repetition of a block of code (e.g., `for`, `while`, `do-while`).

Benefits of Structured Programming

• Improved code readability and maintainability.
• Reduced complexity and easier debugging.
• More reliable and robust programs.
• Facilitates modular design and code reuse.

Writing Efficient Pseudo Code

Pseudo code is an informal way of describing an algorithm. It uses a combination of natural language and structured programming constructs to outline the steps of a program. Writing efficient pseudo code involves:

1. Using clear and concise language.
2. Employing appropriate indentation to show the structure of the algorithm.
3. Avoiding unnecessary complexity.
4. Using consistent naming conventions.

Control Flow Structures in Pseudo Code

Sequence

Sequence is the simplest control flow structure. Instructions are executed one after the other.

Example:

Step	Description
1	Start the program.
2	Read input.
3	Process the input.
4	Display the output.
5	End the program.

Selection (if-else)

The `if-else` statement allows the program to execute different blocks of code based on a condition.

Example:

Step	Description
1	Start the program.
2	Read a number.
3	IF the number is positive:
4	Display "Positive".
5	ELSE:
6	Display "Non-positive".
7	End the program.

Iteration (For Loop)

The `for` loop allows a block of code to be executed repeatedly a specified number of times.

Example:

Step	Description
1	Start the program.
2	Initialize a counter variable to 1.
3	FOR the counter variable from 1 to 10:
4	Display the value of the counter.
5	END FOR
6	End the program.

Iteration (While Loop)

The `while` loop allows a block of code to be executed repeatedly as long as a specified condition is true.

Example:

Step	Description
1	Start the program.
2	Initialize a counter variable to 1.
3	WHILE the counter variable is less than or equal to 10:
4	Display the value of the counter.
5	Increment the counter variable by 1.
6	END WHILE
7	End the program.

Example: Calculating the Factorial of a Number

Let's illustrate with an example of calculating the factorial of a number using pseudo code.

Step	Description
1	Start the program.
2	Read an integer number (n).
3	IF n is less than 0:
4	Display "Factorial is not defined for negative numbers".
5	ELSE:
6	Set factorial = 1.
7	FOR i from 1 to n:
8	Set factorial = factorial * i.
9	END FOR
10	Display the value of factorial.
11	End the program.