Sequence
Sequence is the simplest programming construct — instructions are executed one after another, in the exact order they are written. Every program has sequence as its foundation.
RECEIVE name FROM KEYBOARD
SEND "Hello, " & name TO DISPLAY
SEND "Welcome to CSZone!" TO DISPLAY
Selection
Selection allows a program to make decisions and take different paths based on a condition. The Edexcel 4CP0 pseudocode uses IF/THEN/ELSE/END IF.
IF…THEN…ELSE
IF score >= 70 THEN
SEND "Distinction" TO DISPLAY
ELSE IF score >= 50 THEN
SEND "Merit" TO DISPLAY
ELSE
SEND "Pass" TO DISPLAY
END IF
Nested Selection
Selection statements can be nested inside one another to handle multiple conditions:
IF age >= 18 THEN
IF hasTicket = TRUE THEN
SEND "Access granted" TO DISPLAY
ELSE
SEND "No ticket" TO DISPLAY
END IF
ELSE
SEND "Under 18 — no entry" TO DISPLAY
END IF
Iteration
Iteration (looping) allows a block of code to be repeated. The Edexcel 4CP0 specification includes three types of loop:
FOR Loop (count-controlled)
Used when you know exactly how many times the loop should run:
FOR count FROM 1 TO 10 DO
SEND count TO DISPLAY
END FOR
WHILE Loop (pre-condition)
Checks the condition before each iteration. May not execute at all if condition is false initially:
SET total TO 0
WHILE total < 100 DO
RECEIVE num FROM KEYBOARD
SET total TO total + num
END WHILE
REPEAT…TIMES Loop
Repeats a block a specified number of times (Edexcel-specific):
REPEAT 5 TIMES
SEND "Hello!" TO DISPLAY
END REPEAT
Choosing the Right Loop
| Loop type | Use when… |
|---|
| FOR | You know exactly how many repetitions are needed |
| WHILE | You check a condition first; loop may not run at all |
| REPEAT…TIMES | You want to repeat a fixed number of times (Edexcel variant) |
📝 Exam Tip: Always close loops with the correct keyword: END FOR for FOR loops, END WHILE for WHILE loops, END REPEAT for REPEAT TIMES. Missing or incorrect closing keywords are common syntax errors.
⚠️ Common Mistakes
- Using a FOR loop when the number of iterations depends on user input — use WHILE instead
- Forgetting END IF after selection — every IF needs an END IF
- Off-by-one errors in FOR loops (e.g. writing 1 TO 9 when you need 1 TO 10)