CASE...OF

• A CASE...OF statement is a multi-way selection structure.
• It compares ONE variable against a list of possible fixed values.
• For each value, you write the statement(s) that should run when the variable equals that value.
• If no value matches, the OTHERWISE branch (if present) runs.

A Real Example — Day of the Week

DECLARE Day : INTEGER
INPUT Day
CASE OF Day
  1 : OUTPUT "Monday"
  2 : OUTPUT "Tuesday"
  3 : OUTPUT "Wednesday"
  4 : OUTPUT "Thursday"
  5 : OUTPUT "Friday"
  6 : OUTPUT "Saturday"
  7 : OUTPUT "Sunday"
  OTHERWISE OUTPUT "Invalid day number"
ENDCASE

If the user enters 3, the program outputs "Wednesday". If they enter 9, none of the labels 1–7 match, so the OTHERWISE branch runs and prints "Invalid day number".

The general shape of a CASE...OF in CIE pseudocode is:

CASE OF <variable>
  <value 1> : <statement 1>
  <value 2> : <statement 2>
  ...
  <value n> : <statement n>
  OTHERWISE <statement>
ENDCASE

• CASE OF <variable> — opens the structure and names the variable to test.
• <value> : <statement> — one line per case. The colon separates the value from the action.
• OTHERWISE <statement> — optional fallback when no value matches.
• ENDCASE — closes the structure (mandatory).

Example: Menu Selection

DECLARE Choice : INTEGER
INPUT Choice
CASE OF Choice
  1 : OUTPUT "New file"
  2 : OUTPUT "Open file"
  3 : OUTPUT "Save file"
  4 : OUTPUT "Print file"
  5 : OUTPUT "Exit"
  OTHERWISE OUTPUT "Unknown option"
ENDCASE

The OTHERWISE clause is the "catch-all" branch. It runs when the variable does not match any of the listed case values.

• OTHERWISE is optional but recommended in real programs.
• It must appear after all case labels, just before ENDCASE.
• Without OTHERWISE, a non-matching value means nothing runs — execution continues after ENDCASE.
• It plays the same role as ELSE in an IF statement.

Example: With and Without OTHERWISE

CASE OF Grade
  'A' : OUTPUT "Excellent"
  'B' : OUTPUT "Good"
  'C' : OUTPUT "Pass"
  OTHERWISE OUTPUT "Unknown grade"
ENDCASE

CASE OF Grade
  'A' : OUTPUT "Excellent"
  'B' : OUTPUT "Good"
  'C' : OUTPUT "Pass"
ENDCASE

If Grade is "F" in the first version, the OTHERWISE runs and prints "Unknown grade". In the second version, nothing happens — the program just moves past ENDCASE. Always including OTHERWISE is a defensive habit that prevents silent bugs.

Both CASE...OF and nested IF can express multi-way decisions, but they shine in different situations.

Same Logic, Two Styles

CASE OF Choice
  1 : OUTPUT "Add"
  2 : OUTPUT "Edit"
  3 : OUTPUT "Delete"
  OTHERWISE OUTPUT "Invalid"
ENDCASE

IF Choice = 1 THEN
  OUTPUT "Add"
ELSE
  IF Choice = 2 THEN
    OUTPUT "Edit"
  ELSE
    IF Choice = 3 THEN
      OUTPUT "Delete"
    ELSE
      OUTPUT "Invalid"
    ENDIF
  ENDIF
ENDIF

Let's trace three real-world CASE...OF programs step by step.

Example 1: Day of the Week

DECLARE Day : INTEGER
Day <- 3
CASE OF Day
  1 : OUTPUT "Mon"
  2 : OUTPUT "Tue"
  3 : OUTPUT "Wed"
  4 : OUTPUT "Thu"
  5 : OUTPUT "Fri"
  OTHERWISE OUTPUT "Weekend"
ENDCASE

• Day is 3 → matches the third case label
• OUTPUT "Wed" runs
• Execution continues after ENDCASE — no other case runs

Example 2: Grade Description (string case labels)

DECLARE Grade : CHAR
Grade <- 'B'
CASE OF Grade
  'A' : OUTPUT "Excellent"
  'B' : OUTPUT "Good"
  'C' : OUTPUT "Pass"
  OTHERWISE OUTPUT "Fail"
ENDCASE

Case labels can be characters or strings, not just integers. Grade = 'B' matches the second case, so "Good" is output.

Example 3: Multiple Statements per Case

DECLARE Op : INTEGER
INPUT Op
CASE OF Op
  1 : OUTPUT "Adding"
      OUTPUT "Enter two numbers"
  2 : OUTPUT "Saving"
      OUTPUT "Enter filename"
  3 : OUTPUT "Quitting"
      OUTPUT "Goodbye"
  OTHERWISE OUTPUT "Invalid operation"
ENDCASE

Each case body can contain several statements. They all run when that case label matches, in the order they appear.

Here are the most important facts about CASE...OF before you tackle the Question Bank.