Computer Science (AS & A Level) · Oct / Nov 2022 · Paper 21 · Question 6

The following pseudocode algorithm attempts to check whether a string is a valid email address. FUNCTION IsValid(InString : STRING) RETURNS BOOLEAN DECLARE Index, Dots, Ats, Others : INTEGER DECLARE NextChar : CHAR DECLARE Valid : BOOLEAN Index ← 1 Dots ← 0 Ats ← 0 Others ← 0 Valid ← TRUE REPEAT NextChar ← MID(InString, Index, 1) CASE OF NextChar '.' : Dots ← Dots + 1 '@' : Ats ← Ats + 1 IF Ats > 1 THEN Valid ← FALSE ENDIF OTHERWISE : Others ← Others + 1 ENDCASE IF Dots > 1 AND Ats = 0 THEN Valid ← FALSE ELSE Index ← Index + 1 ENDIF UNTIL Index > LENGTH(InString) OR Valid = FALSE IF NOT (Dots >= 1 AND Ats = 1 AND Others > 8) THEN Valid ← FALSE ENDIF RETURN Valid ENDFUNCTION

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