A program needs to repeatedly accept temperature readings until a valid reading is entered. A valid temperature is between -50 and 60 degrees Celsius. (a) W...

(a) The WHILE loop version uses a flag variable to control repetition. The flag is initially FALSE, and the loop body prompts for input, validates it, and sets the flag to TRUE when the temperature is in range: [4]

DECLARE Temperature : REAL
DECLARE Valid : BOOLEAN

Valid ← FALSE
WHILE Valid = FALSE DO
    OUTPUT "Enter temperature (-50 to 60): "
    INPUT Temperature
    IF Temperature >= -50 AND Temperature <= 60 THEN
        Valid ← TRUE
    ELSE
        OUTPUT "Invalid temperature. Try again."
    ENDIF
ENDWHILE
OUTPUT "Temperature recorded: ", Temperature

[1 mark for WHILE loop with correct condition, 1 mark for input inside loop, 1 mark for validation check, 1 mark for error message and flag update]

(b) The REPEAT...UNTIL version tests the condition after the body, guaranteeing the prompt runs at least once: [2]

REPEAT
    OUTPUT "Enter temperature (-50 to 60): "
    INPUT Temperature
    IF Temperature < -50 OR Temperature > 60 THEN
        OUTPUT "Invalid temperature. Try again."
    ENDIF
UNTIL Temperature >= -50 AND Temperature <= 60
OUTPUT "Temperature recorded: ", Temperature

[1 mark for REPEAT...UNTIL structure, 1 mark for correct exit condition]

(c) The WHILE loop tests its condition before the loop body executes, so if the condition is already FALSE at the start, the body never runs at all. [1] The REPEAT...UNTIL loop always executes the body at least once before testing the condition. For input validation this is more natural because the user must enter a value before it can be checked. [1]