IGCSE / O Level Strings

• A string is a sequence of characters (letters, digits, symbols) treated as text.
• String literals are written inside double quotes, e.g. "Hello".
• Declare a string variable with DECLARE Name : STRING.
• Assign a value using the <- operator.
• The first character is at position 1 (1-indexed in CIE pseudocode).

DECLARE Name : STRING
Name <- "Alice"
OUTPUT Name
OUTPUT "Hello, " + Name

• LENGTH(S) returns the number of characters in S.
• UCASE(S) returns S with all letters in uppercase.
• LCASE(S) returns S with all letters in lowercase.
• These functions return a value — assign to a variable or use in OUTPUT.

DECLARE Word : STRING
Word <- "Hello"
OUTPUT LENGTH(Word)     // 5
OUTPUT UCASE(Word)      // HELLO
OUTPUT LCASE(Word)      // hello

• The + operator joins (concatenates) two strings into one.
• Order matters: A + B is not the same as B + A.
• Concatenation does not add a space automatically.
• You can mix string variables and string literals freely.

DECLARE FirstName, LastName, FullName : STRING
FirstName <- "John"
LastName <- "Smith"
FullName <- FirstName + " " + LastName
OUTPUT FullName   // John Smith

• SUBSTRING(S, Start, Length) extracts Length characters from S starting at position Start.
• Start is 1-indexed — position 1 is the first character.
• The result is a new string; the original variable is unchanged.
• Use SUBSTRING to extract initials, file extensions, or area codes.

DECLARE S, Sub : STRING
S <- "COMPUTER"
Sub <- SUBSTRING(S, 2, 4)   // "OMPU"
OUTPUT Sub
OUTPUT SUBSTRING(S, 1, 3)   // "COM"

• = returns TRUE if two strings are identical.
• <> returns TRUE if two strings are different.
• Comparison is case-sensitive: "abc" is not equal to "ABC".
• For case-insensitive comparison, apply UCASE (or LCASE) to both sides.

DECLARE Password : STRING
INPUT Password
IF UCASE(Password) = "SECRET" THEN
  OUTPUT "Access granted"
ELSE
  OUTPUT "Access denied"
ENDIF

• Username validation — check LENGTH(Username) >= 6.
• Initials extraction — UCASE(SUBSTRING(Name, 1, 1)).
• Password check — compare against a stored value with UCASE().

DECLARE Username : STRING
INPUT Username
IF LENGTH(Username) >= 6 THEN
  OUTPUT "Valid username"
ELSE
  OUTPUT "Too short"
ENDIF

DECLARE First, Last, Initials : STRING
INPUT First
INPUT Last
Initials <- UCASE(SUBSTRING(First, 1, 1))
Initials <- Initials + UCASE(SUBSTRING(Last, 1, 1))
OUTPUT Initials

Recap of every string concept covered in this topic — memorise these and you will be ready for any IGCSE / O Level strings question.