Arrays, lists and records

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Notes de leçon

Arrays and lists

An array stores multiple values of the same data type under one name. Each item has an index (usually starting at 0). Example: scores = [12, 8, 15]; scores[0] is 12.
One-dimensional (1D) arrays are lists; two-dimensional (2D) arrays are tables with rows and columns: grid[row][column].
Arrays have a fixed size in many languages; lists may grow.

Indexed array

Using arrays

Traversal visits elements using their valid indices. For total = 0 and scores = [12, 8, 15], an inclusive FOR loop from 0 to 2 adds all three elements to give 35.
Initialise an accumulator before adding values. For a maximum search, initialise from the first element of a non-empty array rather than assuming zero is a valid starting maximum.

Array traversal

Records

A record groups named fields about one entity, such as a student’s name, age and grade. Fields may have different types.
Collections of records may be held in files or database tables; not every record file by itself is a database system.

When to use

Use arrays for lists of the same type; records for related fields of different types.

Advantages

Arrays avoid many separate variables, make code shorter and loops possible.

Two-dimensional arrays

grid[row][column]
Rows and columns
Nested loops

Accessing a two-dimensional array

Diapos

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Questions d'entraînement

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1.What is an array?
Easy
- Aa data structure storing multiple values under one name
- Ba variable only
- Ca loop
- Da function
2.What is an index?
Easy
- Athe position of an item in an array
- Bthe value
- Cthe size
- Dan error
3.With zero-based indexing, which index selects the first item?
Easy
- A0
- B1
- C-1
- D2
4.What is a record?
Easy
- Aa collection of fields about one thing
- Ba list of numbers
- Ca loop
- Da file name
5.What is a field?
Easy
- Aone item of data in a record
- Ba loop
- Ca function
- Dan array
6.If names = ["Ali","Bo","Cy"], what is names[2]?
Easy
- A"Cy"
- B"Bo"
- C"Ali"
- Derror
7.What is the length of [4, 7, 9, 2]?
Easy
- A4
- B3
- C5
- D2
8.a is a zero-based array of three numbers. What does this inclusive loop do? total = 0; FOR i = 0 TO 2; total = total + a[i]; NEXT i
Easy
- Aadds all three elements
- Bdeletes elements
- Csorts them
- Dfinds the largest

Plus de questions

9.Which is used to process every item in an array?
Easy
- Aa FOR loop
- Ban IF only
- CINPUT
- DOUTPUT
10.What is the value of grid[0][1] in [[1,2],[3,4]]?
Easy
- A2
- B1
- C3
- D4
11.What does a 2D array look like?
Easy
- Aa table
- Ba single line
- Ca loop
- Da circle
12.What is the output? a = [3, 1, 4] OUTPUT a[0] + a[2]
Medium
- A7
- B4
- C8
- D5
13.What is the output? a = [5, 3, 8] largest = a[0] FOR i = 1 TO 2 IF a[i] > largest THEN largest = a[i] ENDIF NEXT i OUTPUT largest
Medium
- A8
- B5
- C3
- D16
14.Using zero-based indexing, what is the resulting array after a[1] = 10 when a = [2, 3, 4]?
Medium
- A[2, 10, 4]
- B[10, 3, 4]
- C[2, 3, 10]
- D[2, 3, 4]
15.Which is a good use of a record?
Medium
- Astoring a student's name, age and grade
- Bstoring 100 temperatures
- Cstoring a single number
- Da loop counter
16.Which is a good use of an array?
Medium
- Astoring 100 temperatures
- Bstoring one name and age
- Ca flowchart
- Da function
17.What does a nested loop process in a 2D array?
Medium
- Aeach row and each column
- Bonly the first row
- Conly the diagonal
- Dnothing
18.How many items are in a 3 by 4 2D array?
Medium
- A12
- B7
- C34
- D3
19.Which loop sets every element of a[0..4] to zero?
Medium
- AFOR i = 0 TO 4 a[i] = 0 NEXT i
- BFOR i = 1 TO 4
- CWHILE i = 0
- DIF a = 0
20.In a bounds-checking language, what occurs when a[10] is accessed in a zero-based array of five elements?
Medium
- Aindex out of range
- Bsyntax error
- Cno error
- Da loop
21.Why use an array rather than 100 variables?
Medium
- Ashorter code and easier processing
- Bfaster hardware
- Cmore memory
- Dno loops
22.What does the number of dimensions of an array specify?
Easy
- Athe number of indexes needed
- Bits size
- Cits type
- Dits name
23.Which statement is true of 1D arrays?
Easy
- Athey use one index
- Bthey use two indexes
- Cthey store tables
- Dthey store records only
24.A table stores one student per row, with name, age and grade columns. What does one row represent?
Medium
- Aone record
- Bone array
- Cone loop
- Done function
25.What does 'traversal' mean?
Medium
- Avisiting each item in turn
- Bdeleting items
- Csorting items
- Dsearching only
26.In a homogeneous array, all elements have the same declared data type.
Easy
True or false?
27.Array indexes often start at 0.
Easy
True or false?
28.A record can only hold numbers.
Easy
True or false?
29.A 2D array can be traversed with nested loops.
Easy
True or false?
30.Accessing an index outside the array is safe.
Medium
True or false?
31.Which are ordinary data fields for a student record?
Medium
- Aname
- Bage
- Cgrade
- DBoolean attendance flag
- EFOR instruction
32.Which tasks use array traversal?
Medium
- Atotalling
- Bfinding the largest
- Csearching
- Dcounting
- Etyping a single input
33.Using zero-based indexing and inclusive FOR bounds, write pseudocode to output every item in a five-element array called names.
Medium

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