Programming Basics (Copy)

1. Introduction to Programming Basics

• Writing a program requires designing a solution and then coding it using appropriate programming tools.
• Key programming tools include:
  • Basic statements
  • Programming constructs
  • Control structures
• Understanding variables, constants, and functions is crucial for structured programming.

2. Constants and Variables

• Constant:
  • A named value that does not change during program execution.
  • Always assigned a value upon declaration.
• Variable:
  • A named value that can change during program execution.
  • Should be declared before use to ensure predictable behavior.
• Best practice:
  • Maintain an identifier list to track declared variables and constants.
  • Assign values to variables before performing operations.
• Some languages, such as Python, do not explicitly support constants, but assigning an initial value ensures intended usage.

3. Declaring Constants and Variables in Pseudocode

• Example of pseudocode for declaring constants and variables:

  DECLARE radius : REAL
  DECLARE volume : REAL
  DECLARE surfaceArea : REAL
  CONSTANT pi ← 3.142
  

• Example algorithm to calculate and output the volume and surface area of a sphere:

  OUTPUT "Please enter the radius of the sphere"
  INPUT radius
  WHILE radius <= 0 DO
      OUTPUT "Please enter a positive number"
      INPUT radius
  ENDWHILE
  volume ← (4 / 3) * pi * radius * radius * radius
  surfaceArea ← 4 * pi * radius * radius
  OUTPUT "Volume is ", volume
  OUTPUT "Surface area is ", surfaceArea
  

• Implementation in different languages:
  • Python: Uses inline variable assignments without explicit declarations.
  • Visual Basic (VB): Requires explicit declarations of variables.
  • Java: Uses final for constants, emphasizing immutability.

4. Library Routines

• Library routines: Predefined functions in a programming language’s development system.
• Advantages:
  • Fully tested and reliable.
  • Enhance efficiency and ease of programming.
• Common standard library functions include:
  • Input/output operations
  • Mathematical computations
  • String manipulation
  • Data structure handling (e.g., sorting, searching)

5. Example of Built-in Functions

• Mathematical operations:
  • DIV(x, y): Returns the integer division result.
  • MOD(x, y): Returns the remainder of division.
• String manipulation functions:
  • LENGTH(anyString): Returns the length of the string.
  • LEFT(anyString, x): Returns the leftmost x characters.
  • RIGHT(anyString, x): Returns the rightmost x characters.
  • MID(anyString, x, y): Extracts y characters from position x.

6. Password Validation Example Using String Functions

• Objective: Check if an input password meets specific criteria.
• Algorithm:

  CONSTANT storedPassword ← "Secret"
  DECLARE inputPassword : STRING
  DECLARE size : INTEGER
  OUTPUT "Please enter your password"
  INPUT inputPassword
  size ← LENGTH(inputPassword)
  IF size = LENGTH(storedPassword) THEN
      IF (LEFT(inputPassword, 1) = LEFT(storedPassword, 1)) AND (RIGHT(inputPassword, 1) = RIGHT(storedPassword, 1)) THEN
          OUTPUT "Password entered has correct first and last letters"
      ELSE
          OUTPUT "Password entered is incorrect"
      ENDIF
  ELSE
      OUTPUT "Password entered is incorrect"
  ENDIF
  

• Implementation Considerations:
  • Case sensitivity should be considered (e.g., checking both uppercase and lowercase versions).
  • Additional security measures like hashing can improve password handling.

7. Summary and Best Practices

• Always declare variables and constants clearly to ensure readability and maintainability.
• Use library routines whenever possible to optimize code efficiency.
• Follow structured programming practices, such as:
  • Using functions and procedures to modularize code.
  • Implementing loops and conditionals effectively.
  • Ensuring clear input and output handling.
• Testing programs thoroughly with different input data, including edge cases.