Structured Programming (Copy)

Introduction to Structured Programming

• Definition:
  • A programming paradigm that emphasizes breaking down a program into smaller, manageable sections, improving readability, maintainability, and reducing errors.
  • It follows principles such as modularity, top-down design, and control structures (sequence, selection, iteration).
• Key Benefits:
  • Enhances code clarity by making it easier to read and debug.
  • Encourages reusability of code components.
  • Reduces redundancy through modular structures.
  • Supports collaborative development by dividing tasks among programmers.
  • Ensures logical organization of code, improving efficiency.

Key Concepts in Structured Programming

1. Procedures

• Definition:
  • A procedure is a reusable block of code that performs a specific task but does not return a value.
  • It is also known as:
    • Void functions in Python
    • Subroutines in VB
    • Methods in Java
• Advantages of Procedures:
  • Avoids repetition by defining a block once and calling it multiple times.
  • Enhances program structure by dividing it into meaningful components.
  • Simplifies debugging and updates.
• Syntax in Pseudocode:

  PROCEDURE <identifier>
     <statements>
  ENDPROCEDURE
  

• Calling a Procedure:

  CALL <identifier>
  

• Example:
  • Procedure to print stars:

  PROCEDURE stars (Number : INTEGER)
     FOR Counter ← 1 TO Number
         OUTPUT "*"
     NEXT Counter
  ENDPROCEDURE
  

2. Functions

• Definition:
  • A function is a block of code similar to a procedure but always returns a value.
  • Known as:
    • Fruitful functions in Python
    • Functions in VB
    • Methods with returns in Java
• Syntax in Pseudocode:

  FUNCTION <identifier> RETURNS <data type>
     <statements>
  ENDFUNCTION
  

• Calling a Function:

  myValue ← <identifier>(parameters)
  

• Example:
  • Function to convert Fahrenheit to Celsius:

  FUNCTION celsius (temperature : REAL) RETURNS REAL
     RETURN (temperature – 32) / 1.8
  ENDFUNCTION
  

• Function vs Procedure:
  

  Feature	Procedure	Function
  Returns a value	No	Yes
  Part of an expression?	No	Yes
  Can modify variables?	Yes (if using reference parameters)	No (generally)

3. Parameters and Arguments

• Parameter:
  • A variable in the function or procedure definition that receives a value.
• Argument:
  • The actual value passed to a function or procedure.

Types of Parameter Passing

1. By Value (ByVal):
   • The procedure/function gets a copy of the value.
   • Changes to the variable do not affect the original value.
   • Default method in Python and Java.
2. By Reference (ByRef):
   • The procedure/function gets the actual memory address of the variable.
   • Changes affect the original variable.
   • Used in VB explicitly with ByRef.

• Example:
  • Procedure to convert Fahrenheit to Celsius using ByRef:

  PROCEDURE celsius(BYREF temperature : REAL)
     temperature ← (temperature – 32) / 1.8
  ENDPROCEDURE
  

4. Modular Programming and Top-Down Design

• Definition:
  • A method of structuring a program where it is broken down into smaller, self-contained modules.
  • Each module (procedure/function) solves a specific part of the problem.
• Example:
  • Main Program
    • Calls a function to read input.
    • Calls a function to process data.
    • Calls a function to display results.

5. Control Structures in Structured Programming

5.1 Sequence

• Definition:
  • The simplest control structure where instructions are executed one after another.
• Example:

  OUTPUT "Enter name"
  INPUT name
  OUTPUT "Hello ", name
  

5.2 Selection (Decision Making)

• Definition:
  • A structure that allows decisions based on conditions.
• Types:
  • IF…THEN…ELSE
  • CASE (Switch Statement)
• Example (IF…THEN…ELSE):

  IF age >= 18 THEN
     OUTPUT "You can vote"
  ELSE
     OUTPUT "You cannot vote"
  ENDIF
  

• Example (CASE Statement):

  CASE OF option
     1: OUTPUT "Option 1 selected"
     2: OUTPUT "Option 2 selected"
  OTHERWISE:
     OUTPUT "Invalid option"
  ENDCASE
  

5.3 Iteration (Loops)

• Definition:
  • Loops are used to repeat a block of code multiple times.
• Types:
  1. FOR…NEXT – Used when the number of iterations is known.
  2. WHILE…DO…ENDWHILE – Used when the condition is checked before entering the loop.
  3. REPEAT…UNTIL – Used when the condition is checked after executing the loop.
• Examples:
  • FOR Loop:

  FOR Counter ← 1 TO 10
     OUTPUT "Hello"
  NEXT Counter
  

  • WHILE Loop:

  WHILE score < 100 DO
     score ← score + 10
  ENDWHILE
  

  • REPEAT Loop:

  REPEAT
     OUTPUT "Enter value"
     INPUT value
  UNTIL value >= 0
  

6. Library Routines

• Definition:
  • Pre-written functions available in a programming language that help with common tasks like:
    • Mathematical operations (e.g., sqrt(), abs())
    • String manipulation (e.g., len(), substring())
    • File handling (e.g., open(), read())
• Advantages:
  • Saves time and effort.
  • Reduces coding errors.
  • Enhances performance.

7. Practical Applications

• Example Application: Car Depreciation Calculation
  • A program to predict a car’s value based on depreciation:
    • First year: 40% depreciation.
    • Each subsequent year: 20% depreciation.
    • Stops when the car is 9 years old or value < $1000.
  • Algorithm Outline:
    1. Get initial car price.
    2. Loop for up to 9 years.
    3. Apply correct depreciation rate.
    4. Display updated car value.
    5. Exit when conditions are met.

Conclusion

• Structured programming ensures clear, efficient, and maintainable code.
• The use of procedures, functions, loops, and selection statements improves modularity.
• Following structured programming principles helps in building large-scale applications with ease.