Write pseudocode statements for: the assignment of values to variables

11.1 Programming Basics – Assignment of Values to Variables

Context & Syllabus Alignment

• Syllabus item: 11.1 Programming Basics (Cambridge International AS & A Level Computer Science 9618).
• This lesson introduces the **assignment** statement, the required pseudocode syntax, the rules for variable names, data‑type compatibility, constants, input/output and built‑in functions.
• Assessment objectives covered:
  • AO1 – Knowledge: definition of assignment, assignment operator, naming rules, type‑compatibility and constant rules.
  • AO2 – Application: write correct pseudocode statements that assign values to variables of different types, including I/O.
  • AO3 – Design & Programming: use assignment correctly inside larger algorithmic structures such as loops and procedures.
• Suggested sequence: data types → literals → declaration & constants → assignment → input/output → control structures → procedures/functions → arrays/records → algorithm design & testing.

Key Terms (as used in the syllabus)

1. Declaration & Constants

Although many exam questions omit explicit declarations, the board expects you to understand the syntax.

RECORD student
    STRING name
    INTEGER mark
END RECORD

2. Assignment Syntax

The assignment operator in Cambridge pseudocode is :=. The general form is:

variable := expression

After execution, variable holds the value produced by expression. A statement may be terminated with a semicolon (;) when the exam specification requires it.

2.1 Rules for Variable Names

• Start with a letter (A–Z or a–z).
• Subsequent characters may be letters, digits (0–9) or an underscore (_).
• Case‑insensitive, but keep the same spelling throughout a program.
• Do not use reserved words (e.g. IF, FOR, PROCEDURE, BEGIN, END).
• Prefer meaningful names that reflect the data stored.

2.2 Data Types, Literals and Implicit Conversions

Only the following implicit conversions are allowed:

All other conversions cause a type error.

2.3 Error Handling in Assignment

• Type error: illegal conversion. Fix: use an explicit conversion function (e.g. INT()) or redesign the expression.
• Uninitialised variable: variable used on the right‑hand side before a value has been given. Fix: initialise at declaration or before first use.
• Out‑of‑range error: value exceeds the permitted range for the target type. Fix: apply rounding/truncation or use a larger type.
• Constant‑assignment error: attempting to assign to a constant. Fix: treat the constant as read‑only.

3. Common Forms of Assignment (with Examples)

3.1 Simple Value Assignment

INTEGER age
age := 18

3.2 Arithmetic Assignment

INTEGER a, b, sum
a := 7
b := 5
sum := a + b   // sum now holds 12

3.3 Compound Assignment (using the variable’s existing value)

INTEGER counter
counter := 0
counter := counter + 1   // increment
counter := counter * 2   // double

3.4 Assignment to Array Elements

INTEGER scores[5]
i := 3
scores[i] := 87   // stores 87 in the 4th element (indexing starts at 0)

3.5 Assignment to Record/ADT Fields

RECORD student
    STRING name
    INTEGER mark
END RECORD

student := NEW student
student.name := "Bob"
student.mark := 73

3.6 Using Expressions

REAL radius, area
radius := 3.5
area := 3.14159 * radius * radius   // πr²

3.7 String Concatenation

STRING firstName, lastName, fullName
firstName := "Ada"
lastName  := "Lovelace"
fullName  := firstName & " " & lastName   // "Ada Lovelace"

3.8 Boolean Assignment

INTEGER score
BOOLEAN isPass
score := 78
isPass := score >= 50   // TRUE

3.9 Multiple Assignment in One Line (if permitted)

a, b, c := 1, 2, 3   // a=1, b=2, c=3

3.10 Assignment Combined with Input / Output (AO2)

INTEGER mark
BOOLEAN passed
READ mark                // input from the user
passed := mark >= 40    // assign result of comparison
WRITE "Passed? ", passed   // output TRUE/FALSE

3.11 Using a Built‑in Function

STRING name
INTEGER length
READ name
length := LEN(name)          // LEN returns the number of characters
WRITE "The name has ", length, " letters."

4. Assignment Inside Larger Structures (AO3)

Below is a compact algorithm that demonstrates declaration, input, assignment, a loop, array usage and output.

PROCEDURE ReadMarksAndTotal
    INTEGER i, total
    INTEGER marks[5]
    total := 0
    FOR i FROM 0 TO 4 DO
        READ marks[i]                 // input each mark
        total := total + marks[i]     // accumulate using assignment
    ENDFOR
    WRITE "Total of the 5 marks = ", total
END PROCEDURE

5. Common Mistakes to Avoid

• Using = instead of := for assignment.
• Assigning a value of an incompatible type (e.g., a string to an integer).
• Attempting to assign to a constant.
• Using a variable on the right‑hand side before it has been given a value.
• Omitting the required semicolon when the exam specification asks for it.
• Assuming illegal implicit conversions are allowed (e.g., string → integer).

6. Practice Exercises

1. Declare an integer variable called counter and initialise it to 0.
2. Read a student's mark (integer) and store TRUE in a Boolean variable passed if the mark is 40 or above.
3. Given REAL length, width, area, assign the product of length and width to area.
4. Create a string variable greeting that concatenates the word “Hello”, a space, and a variable name (which already holds a student's name).
5. Using a single assignment statement, set three integer variables x, y, z to the values 10, 20, and 30 respectively.
6. Assign the value 0 to every element of an integer array marks[5] using a loop.
7. Given a record student with fields name (STRING) and score (INTEGER), write pseudocode that updates student.score to the value stored in variable newScore.
8. Write a short program that reads a string word, uses the built‑in function LEN() to find its length, and writes “Length = ” followed by the length.
9. Extend the algorithm in section 4 to also calculate and write the average mark (as a REAL).