Basic Constructs
1. Selection
Selection allows the program to choose different paths based on a condition.
IF ... THEN ... ELSE
Used for binary choices (Yes/No).
IF Mark >= 50 THEN
OUTPUT "Pass"
ELSE
OUTPUT "Fail"
ENDIF
OUTPUT "Pass"
ELSE
OUTPUT "Fail"
ENDIF
CASE ... OF
Efficient for multiple discrete choices (e.g., a menu).
CASE Choice OF
1 : CALL AddRecord()
2 : CALL DeleteRecord()
3 : CALL ViewRecord()
OTHERWISE OUTPUT "Invalid Choice"
ENDCASE
1 : CALL AddRecord()
2 : CALL DeleteRecord()
3 : CALL ViewRecord()
OTHERWISE OUTPUT "Invalid Choice"
ENDCASE
2. Iteration (Loops)
Iteration is used to repeat a block of code multiple times.
FOR ... TO ... NEXT
Count-controlled: Used when you know exactly how many times the loop should run.
FOR Count ← 1 TO 10
OUTPUT "Iteration: ", Count
NEXT Count
OUTPUT "Iteration: ", Count
NEXT Count
REPEAT ... UNTIL
Post-condition: The condition is checked at the end. The loop always runs at least once.
REPEAT
OUTPUT "Enter a positive number"
INPUT Num
UNTIL Num > 0
OUTPUT "Enter a positive number"
INPUT Num
UNTIL Num > 0
WHILE ... DO ... ENDWHILE
Pre-condition: The condition is checked at the start. If the condition is false initially, the loop never runs.
WHILE Answer <> "Exit" DO
INPUT Answer
ENDWHILE
INPUT Answer
ENDWHILE
3. Comparison Table: Which Loop to Use?
| Loop Type | Best Used For... | Min. Iterations |
|---|---|---|
| FOR | Fixed number of repetitions. | Defined by range |
| REPEAT | Validation (checking input). | 1 |
| WHILE | Reading files or unknown repetitions. | 0 |
⚠️ Exam Note: Make sure to close your constructs! Every
IF needs an ENDIF, every WHILE needs an ENDWHILE, and every CASE needs an ENDCASE.