1D Arrays & 1-Based Indexing

A One-Dimensional (1D) Array is a static data structure holding a fixed collection of elements of the same data type, referenced under a single identifier and accessed via an integer index.

1. Array Declaration in Cambridge Pseudocode

DECLARE <Identifier> : ARRAY[<LowerBound>:<UpperBound>] OF <DataType>

Key Declaration Rules:

• Enclose the bounds inside square brackets [...].
• Separate lower and upper bounds with a colon :.
• Follow the declared bounds; [1:50] has 50 elements and [0:49] also has 50.
• Specify the type with the OF keyword (e.g. OF INTEGER, OF STRING).

2. Accessing and Manipulating Array Elements

Individual elements are read or written using square bracket index notation:

DECLARE Grades : ARRAY[1:5] OF CHAR

// Direct assignment
Grades[1] <- 'A'
Grades[2] <- 'B'

// Iterative input
FOR i <- 1 TO 5
    INPUT Grades[i]
NEXT i

Exam Warning: Attempting to read or write to Grades[0] or Grades[6] triggers an Array Index Out of Bounds runtime error.

Declared bounds matter

Arrays can be declared with different lower bounds. ARRAY[0:4] contains five elements just as ARRAY[1:5] does. Use the declared bounds in loops; index zero is not universally forbidden. Our examples usually start at 1 for consistency.