Programming Concepts (Copy)

1. Declaring and Using Variables and Constants

• Variable
  • A named storage location in memory whose value can change during program execution.
  • Each variable has:
    • A name (identifier)
    • A data type
    • A value
  • Example in pseudocode:

    DECLARE age : INTEGER
    age ← 16
    age ← age + 1
    

  • Purpose: Used for storing values that may be updated or recalculated.
• Constant
  • A named value that does not change during program execution.
  • Improves program maintainability — changes made to the constant definition affect all occurrences.
  • Example in pseudocode:

    CONSTANT Pi = 3.14159
    area ← Pi * radius^2
    

• Declaration rules:
  • Variables must be declared before they are used (depending on language).
  • Constants are declared once, then used without modification.

2. Basic Data Types

• Integer
  • Whole numbers, positive or negative, without decimal points.
  • Examples: −15, 0, 27
  • Pseudocode declaration:

    DECLARE score : INTEGER
    

• Real
  • Numbers with fractional parts (decimals).
  • Examples: 3.14, −0.5, 10.0
  • Pseudocode:

    DECLARE temperature : REAL
    

• Char (Character)
  • Single alphanumeric character or symbol.
  • Stored inside single quotes.
  • Examples: ‘A’, ‘7’, ‘%’
  • Pseudocode:

    DECLARE grade : CHAR
    

• String
  • Sequence of characters.
  • Stored inside double quotes.
  • Examples: “Hello”, “CS2210”
  • Pseudocode:

    DECLARE name : STRING
    

• Boolean
  • Logical data type that can hold only two values: TRUE or FALSE.
  • Example:

    DECLARE isLoggedIn : BOOLEAN
    

3. Input and Output

• Input – Reading data from the user or an external source.
  • Example in pseudocode:

    OUTPUT "Enter your name: "
    INPUT name
    

• Output – Displaying data to the screen or writing to a file.
  • Example in pseudocode:

    OUTPUT "Welcome ", name
    

• Purpose:
  • Input allows interaction between the user and the program.
  • Output provides feedback and results.

4. Sequence, Selection, Iteration, Totalling, and Counting

(a) Sequence

• Execution of instructions one after another in the order they are written.
• No branching or looping.
• Example:

  INPUT length
  INPUT width
  area ← length * width
  OUTPUT area
  

(b) Selection

• Execution of different code depending on a condition.
• IF statements:

  IF age >= 18 THEN
      OUTPUT "Adult"
  ELSE
      OUTPUT "Minor"
  ENDIF
  

• CASE statements:

  CASE grade OF
      "A": OUTPUT "Excellent"
      "B": OUTPUT "Good"
      "C": OUTPUT "Pass"
      OTHERWISE OUTPUT "Fail"
  ENDCASE
  

(c) Iteration

• Repeating a block of code multiple times.
• Count-controlled loop:

  FOR i ← 1 TO 10
      OUTPUT i
  NEXT i
  

• Pre-condition loop (WHILE):

  WHILE answer <> "yes"
      INPUT answer
  ENDWHILE
  

• Post-condition loop (REPEAT UNTIL):

  REPEAT
      INPUT number
  UNTIL number > 0
  

(d) Totalling

• Adding up values over iterations.
• Example:

  total ← 0
  FOR i ← 1 TO 5
      INPUT mark
      total ← total + mark
  NEXT i
  OUTPUT total
  

(e) Counting

• Keeping track of how many times a condition occurs.
• Example:

  count ← 0
  FOR i ← 1 TO 5
      INPUT mark
      IF mark >= 50 THEN
          count ← count + 1
      ENDIF
  NEXT i
  OUTPUT count
  

5. String Handling

• Length function: Returns number of characters in a string.

  length ← LENGTH("Hello")   // returns 5
  

• Substring: Extracts part of a string.

  sub ← SUBSTRING("Computer", 1, 4)   // returns "Comp"
  

  • Starting position can be 0 or 1 depending on language.
• Upper: Converts string to uppercase.

  UPPER("hello")   // returns "HELLO"
  

• Lower: Converts string to lowercase.

  LOWER("HELLO")   // returns "hello"
  

6. Arithmetic, Logical, and Boolean Operators

Arithmetic Operators:

• + (Addition)
• − (Subtraction)
• / (Division)
• * (Multiplication)
• ^ (Power of, e.g., 2^3 = 8)
• MOD (Modulus – remainder after division)
• DIV (Integer division – quotient without remainder)

Logical Operators:

• = (Equal to)
• < (Less than)
• <= (Less than or equal to)
• > (Greater than)
• >= (Greater than or equal to)
• <> (Not equal to)

Boolean Operators:

• AND (True if both conditions are true)
• OR (True if at least one condition is true)
• NOT (Reverses logical value)

7. Nested Statements

• Selection or iteration statements inside other selection or iteration blocks.
• Nested selection example:

  IF grade = "A" THEN
      OUTPUT "Excellent"
  ELSE
      IF grade = "B" THEN
          OUTPUT "Good"
      ELSE
          OUTPUT "Needs improvement"
      ENDIF
  ENDIF
  

• Nested iteration example:

  FOR i ← 1 TO 3
      FOR j ← 1 TO 2
          OUTPUT i, j
      NEXT j
  NEXT i
  

8. Procedures, Functions, and Parameters

• Procedure:
  • A reusable block of code that performs a task but does not return a value.
  • Example:

    PROCEDURE DisplayMenu()
        OUTPUT "1. Start"
        OUTPUT "2. Exit"
    ENDPROCEDURE
    

• Function:
  • A reusable block of code that returns a value.
  • Example:

    FUNCTION Square(x : INTEGER) RETURNS INTEGER
        RETURN x * x
    ENDFUNCTION
    

• Parameters:
  • Data passed into a procedure or function.
  • Can be with parameters or without parameters.
  • Max two parameters in syllabus requirements.
• Local Variables:
  • Declared inside a procedure/function.
  • Only accessible within that procedure/function.
• Global Variables:
  • Declared outside all procedures/functions.
  • Accessible by all parts of the program.

9. Library Routines

• Pre-written and built-in functions in the programming language.
• Examples:
  • MOD – Modulus
  • DIV – Integer division
  • ROUND – Round decimal to nearest integer
  • RANDOM – Generates random number

10. Creating Maintainable Programs

• Meaningful Identifiers:
  • Names that describe their purpose.
  • Example: studentName instead of x1.
• Commenting:
  • Use comments to explain purpose of code sections.
  • Syntax depends on language (e.g., // or REM).
• Procedures and Functions:
  • Divide code into smaller parts to improve readability.
• Consistent Formatting:
  • Indentation, spacing, and naming conventions.