AS · Practice questions · Variables, constants and built-in functions

Every statement exact.

Six original Cambridge-style questions on variables, constants, expressions and built-in functions, with mark points.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Literal, operator, function.

Constant: CONSTANT Name = literal, declared at the start, never assigned again.
Division: / gives a REAL; DIV gives the whole-number quotient; MOD gives the remainder.
Strings: positions start at 1; MID(s, start, length); join with &.
Random integers: INT(RAND(n)) gives 0 to n − 1; add the lowest value you want.

Recall

[2 marks]

Explain the difference between a variable and a constant.

A variable is a named memory location whose value can change while the program runs. ✓
A constant is given a (literal) value when it is declared and that value cannot change while the program runs. ✓

Calculate

[4 marks]

A holds 23 and B holds 4. Give the value of each expression.

(a) A DIV B (b) A MOD B (c) A / B (d) (A > 20) AND (B MOD 2 = 1)

(a) 5 ✓
(b) 3 ✓
(c) 5.75 ✓
(d) FALSE: A > 20 is TRUE but 4 MOD 2 = 0, so B MOD 2 = 1 is FALSE, and TRUE AND FALSE is FALSE. ✓

Convert

[4 marks]

Write pseudocode for this structured English. Declare everything you use.

1. SET Pi to 3.142 (this value never changes)
2. INPUT the radius of a circle
3. CALCULATE the area as Pi multiplied by the radius squared
4. OUTPUT a message and the area

CONSTANT Pi = 3.142 ✓
DECLARE Radius : REAL and DECLARE Area : REAL ✓
INPUT Radius and Area ← Pi * Radius * Radius ✓
OUTPUT "Area is ", Area ✓

Apply

[3 marks]

Code holds the string "CS9618-AS". State the value returned by:

(a) LENGTH(Code) (b) MID(Code, 3, 4) (c) RIGHT(Code, 2)

(a) 9 ✓
(b) "9618" ✓
(c) "AS" ✓

Write

[5 marks]

A full name such as Ada Lovelace contains exactly one space. Write pseudocode that inputs a full name and outputs the initials, for example AL. Use the functions LENGTH and MID.

Declare FullName, Initials (STRING) and Index (INTEGER); INPUT FullName. ✓
Initials ← MID(FullName, 1, 1) to take the first letter. ✓
FOR Index ← 2 TO LENGTH(FullName) ... NEXT Index. ✓
IF MID(FullName, Index, 1) = " " THEN Initials ← Initials & MID(FullName, Index + 1, 1) with ENDIF. ✓
OUTPUT Initials after the loop. ✓

Write

[3 marks]

Write pseudocode to generate a random whole number from 10 to 20 inclusive, store it in Number, and output Even or Odd as appropriate.

Number ← INT(RAND(11)) + 10 (RAND(11) gives 0 to below 11, INT gives 0 to 10). ✓
IF Number MOD 2 = 0 THEN ✓
OUTPUT "Even" ELSE OUTPUT "Odd" ENDIF. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.