Aqa Pseudo-code syntax

Question 1

IntExp, RealExp, BoolExp, CharExp and StringExp mean

Answer 1

IntExp, RealExp, BoolExp, CharExp and StringExp mean any expression which can be evaluated to an integer, real, Boolean (False or True), character or string respectively.

Question 2

Exp means

Answer 2

Any expression

Question 3

Emboldened pseudo-code is used

Answer 3

Used to indicate the keywords/operators

Question 4

Exam paper questions will assume that indexing for arrays and strings start at __

Answer 4

0 unless specifically stated otherwise.

Question 5

Single line comments

Answer 5

comment

Question 6

Multi-line comments

Answer 6

# comment
# comment and so on

Question 7

Variable assignment

Answer 7

Identifier ← Exp

a← 3
b ← a + 1
c ← ‘Hello’

Question 8

Constant assignment

Answer 8

CONSTANT IDENTIFIER ← Exp

CONSTANT PI ← 3.141 CONSTANT CLASS_SIZE ← 23
# Names of constants will always be
# written in capitals

Question 9

Standard arithmetic operations (4)

Answer 9

*
/

Used in the normal way with brackets to indicate precedence where needed. For example, a + b * c would multiply b and c together and then add the result to a, whereas (a + b) * c would add a and b together and then multiply the result by c.

Question 10

Integer division

Answer 10

IntExp DIV IntExp

Question 11

9 DIV 5
5 DIV 2
8 DIV 4

Answer 11

evaluates to 1
evaluates to 2
evaluates to 2

Question 12

Modulus operator

Answer 12

IntExp MOD IntExp

Question 13

9 MOD 5
5 MOD 2
8 MOD 4

Answer 13

evaluates to 4
evaluates to 1
evaluates to 0

Question 14

Relational operators for types that can be clearly ordered:

Less than - 
Greater than - 
Equal to - 
Not equal to - 
Less than or equal to -  Greater than or equal to -

Answer 14

Exp < Exp
   Exp > Exp
   Exp = Exp
   Exp ≠ Exp
   Exp ≤ Exp
   Exp ≥ Exp

Question 15

Examples of:

Less than - 
Greater than - 
Equal to - 
Not equal to - 
Less than or equal to -  Greater than or equal to -

Answer 15

4 <6
'A' < 'B' 
'adam' < 'adele'
4.1 > 4.0 
3= 3
qty ≠ 7
3 ≤4 
4 ≤4
4≥ 3 
4.5 ≥ 4.5

Question 16

What is greater, and why?

‘adam’ ‘adele’

Answer 16

‘adam’ < ‘adele’

Alphabetically, ‘a’ comes before ‘d’, whichever first letter is different

Question 17

Boolean operations

Logical AND
Logical OR
Logical NOT

Answer 17

BoolExp AND BoolExp
BoolExp OR BoolExp
NOT BoolExp

(3 = 3) AND (3 ≤ 4)
(x < 1) OR (x > 9)
NOT (a < b)

Question 18

Indefinite (condition controlled) iteration

REPEAT-UNTIL (repeat the statements until the Boolean expression is True)

Answer 18

REPEAT
# statements here UNTIL BoolExp

a←1
REPEAT 
   OUTPUT a
    a←a+1 
UNTIL a = 4

will output 1, 2, 3

Question 19

Indefinite (condition controlled) iteration

WHILE

Answer 19

WHILE BoolExp
# statements here
ENDWHILE

a←1
WHILE a < 4
  OUTPUT a
   a←a+1 
ENDWHILE
# will output 1, 2, 3

Question 20

Definite (count controlled) iteration

FOR-TO-[STEP]- ENDFOR
If STEP IntExp is missing it is considered to be 1.

Answer 20

FOR Identifier ← IntExp TO IntExp [STEP IntExp]
# statements here
ENDFOR
# If STEP IntExp is omitted the step value is 1.

Question 21

FOR a ← 1 TO 3
OUTPUT a
ENDFOR

What will this output?

Answer 21

will output 1, 2, 3

Question 22

FOR a ← 1 TO 5 STEP 2
OUTPUT a
ENDFOR

What will this output?

Answer 22

will output 1, 3, 5

Question 23

FOR-IN-ENDFOR (repeat the statements the number of times that there are characters
in a string)

Answer 23

FOR Identifier IN StringExp
# statements here
ENDFOR

Question 24

Pseudocde to calculate the numbers of characters in message

Answer 24

length ← 0
FOR char IN message
length ←length +1
ENDFOR

# will calculate the
# number of characters
# in message

Question 25

Pseudocde to output a string in revere

Answer 25

``` reversed ← '' FOR char IN message reversed ← char + reversed ENDFOR OUTPUT reversed ``` will output the string in reverse

Question 26

SELECTION IF-THEN-ELSE-ENDIF (execute the statements following the THEN if the Boolean expression is True, otherwise execute the statements following the ELSE)

Answer 26

IF BoolExp THEN # statements here ENDIF ``` a← 1 IF (a MOD 2) = 0 THEN OUTPUT ‘even’ ELSE OUTPUT ‘odd’ ENDIF ```

Question 27

NESTED IF-THEN-ELSE ENDIF (use nested versions of the above to create more complex conditions) Note that IF statements can be nested inside the THEN part, the ELSE part or both

Answer 27

``` IF BoolExp THEN # statements here ELSE IF BoolExp THEN # statements here ELSE # statements here ENDIF ENDIF ```

Question 28

IF-THEN-ELSE IF ENDIF (removes the need for multiple indentation levels)

Answer 28

``` IF BoolExp THEN # statements here ELSE IF BoolExp THEN # statements here # possibly more ELSE ELSE # statements here ENDIF ```

Question 29

ARRAYS ASSIGNMENT

Answer 29

Identifier ← [Exp, ... ,Exp] | primes ← [2, 3, 5, 7, 11, 13]

Question 30

Arrays | Accessing an elemenT

Answer 30

Identifier[IntExp]

Question 31

primes ← [2, 3, 5, 7, 11, 13] | primes[0]

Answer 31

evaluates to 2 (questions on exam papers will start indexing at 0 unless specifically stated otherwise)

Question 32

Arrays | Updating an element

Answer 32

Identifier[IntExp] ← Exp primes ← [2, 3, 5, 7, 11, 13] ``` primes[5] ← 17 # array is now [2, 3, 5, 7, 11, 17] ```

Question 33

Accessing an element in a two-dimensional array

Answer 33

Identifier[IntExp (row)][IntExp (column)]

Question 34

table ← [[1, 2],[2, 4],[3, 6],[4, 8]] table[3][1]

Answer 34

``` # evaluates to 8 as second element # (with index 1) of fourth array # (with index 3) in table is 8 ```

Question 35

Updating an element in a two- dimensional array

Answer 35

Identifier[IntExp][IntExp] ← Exp

Question 36

table ← [[1, 2],[2, 4],[3, 6],[4, 8]] table[3][1] ← 16

Answer 36

table[3][1] ← 16 ``` # table is now #[ [1, 2], # [2, 4], # [3, 6], # [4, 16] ] ```

Question 37

Array length

Answer 37

LEN(Identifier)

Question 38

table ← [[1, 2],[2, 4],[3, 6],[4, 8]] LEN(table)

Answer 38

evaluates to 4

Question 39

table ← [[1, 2],[2, 4],[3, 6],[4, 8]] LEN(table[0])

Answer 39

Evaluates to 2

Question 40

FOR-IN-ENDFOR (repeat the statements the number of times that there are elements in an array) NOTE: array items cannot be modified using this method

Answer 40

FOR Identifier IN array # statements here ENDFOR ``` primes ← [2, 3, 5, 7, 11, 13] total ← 0 FOR prime IN primes total ← total + prime ENDFOR OUTPUT 'Sum of the values in primes is' OUTPUT total ```

Question 41

Record declaration pseudo-code

Answer 41

RECORD Record_identifier field1 : field2 : ... ENDRECORD

Question 42

Record for a car declaration: make, model, reg, price, noOfDoors

Answer 42

``` RECORD Car make : String model : String reg : String price : Real noOfDoors : Integer ENDRECORD ```

Question 43

Pseudo-code record variable initialisation

Answer 43

varName ← Record_identifier(value1, value2, ...)

Question 44

``` RECORD Car make : String model : String reg : String price : Real noOfDoors : Integer ``` Initialise a ford: pseudo-code

Answer 44

myCar ← Car('Ford', 'Focus', 'DX17 | GYT', 1399.99, 5)

Question 45

Assigning a value to a field in a record - pseudo-code

Answer 45

varName.field ← Exp

Question 46

myCar ← Car('Ford', 'Focus', 'DX17 GYT', 1399.99, 5) Change model to fiesta, pseudo-code

Answer 46

``` myCar.model ←'Fiesta' # The model field of the myCar # record is assigned the value # 'Fiesta'. ```

Question 47

Accessing values of fields within records - pseudocode

Answer 47

varName.field

Question 48

What does this do? (Records topic) OUTPUT myCar.model

Answer 48

OUTPUT myCar.model ``` # Will output the value stored in the # model field of the myCar record ```

Question 49

Difference between subroutines and functions in pseudo-code

Answer 49

for the purposes of this pseudo-code definition subroutines that contain a RETURN keyword are functions. Those that do not contain a RETURN keyword are procedures.

Question 50

Subroutine definition

Answer 50

``` SUBROUTINE Identifier(parameters) # statements here ENDSUBROUTINE ```

Question 51

Subroutine to add two numbers

Answer 51

SUBROUTINE showAdd(a, b) result ← a + b OUTPUT result END SUBROUTINE

Question 52

SUBROUTINE sayHi() OUTPUT ‘Hi’ ENDSUBROUTINE Function or procedure?

Answer 52

Procedure

Question 53

SUBROUTINE add(a, b) result ← a + b RETURN result Function or procedure?

Answer 53

Function

Question 54

Calling subroutines without a return value

Answer 54

Identifier(parameters) | showAdd(2, 3)

Question 55

Calling subroutines with a return value

Answer 55

identifier ← identifier(parameters) answer ← add(2, 3)

Question 56

String length pseudo-code

Answer 56

LEN(StringExp)

Question 57

LEN('computer science')

Answer 57

evaluates to 16(including space)

Question 58

Position of a character

Answer 58

POSITION(StringExp, CharExp)

Question 59

POSITION('computer science', 'm')

Answer 59

``` # evaluates to 2 (as with arrays # exam papers will start # indexing at 0 unless # specifically stated otherwise) ```

Question 60

Substring

Answer 60

Substring (the substring is created by the first parameter indicating the start position within the string, the second parameter indicating the final position within the string and the third parameter being the string itself). SUBSTRING(IntExp, IntExp, StringExp)

Question 61

SUBSTRING(2, 9, 'computer science')

Answer 61

evaluates to 'mputer s'

Question 62

Concatenation

Answer 62

StringExp + StringExp

Question 63

'computer' + 'science'

Answer 63

evaluates to 'computerscience'

Question 64

String and character conversion: ``` Converting string to integer - Converting string to real - Converting integer to string - Converting real to string - Converting character to character code - Converting character code to character - ```

Answer 64

``` STRING_TO_INT(StringExp) STRING_TO_REAL(StringExp) INT_TO_STRING(IntExp) REAL_TO_STRING(RealExp) CHAR_TO_CODE(CharExp) CODE_TO_CHAR(IntExp) ```

Question 65

STRING_TO_INT('16') STRING_TO_REAL('16.3') 16.3 INT_TO_STRING(16) REAL_TO_STRING(16.3) CHAR_TO_CODE('a') CODE_TO_CHAR(97)

Answer 65

``` STRING_TO_INT('16') # evaluates to the integer 16 STRING_TO_REAL('16.3') # evaluates to the real 16.3 INT_TO_STRING(16) # evaluates to the string '16' REAL_TO_STRING(16.3) # evaluates to the string '16.3' CHAR_TO_CODE('a') # evaluates to 97 using ASCII/Unicode CODE_TO_CHAR(97) # evaluates to 'a' using ASCII/Unicode ```

Question 66

User input

Answer 66

USERINPUT a ← USERINPUT

Question 67

Output

Answer 67

OUTPUT a OUTPUT a, g The output statement can be followed by multiple StringExp separated by commas

Question 68

Random integer generation

Answer 68

Random integer generation (between two integers inclusively) Identifier ← RANDOM_INT(IntExp, IntExp)

Question 69

diceRoll ← RANDOM_INT(1, 6)

Answer 69

Will randomly generate an integer between 1 and 6 inclusive