← IGCSE Computer Science Paper 2

Declaring a variable to hold file data

Creates a variable named LineOfText that holds text. Declare it before the file commands that use it, for example before READFILE stores a line in it.

Part of: IGCSE Computer Science 0478 — 8.3 File Handling — Module 4

Understanding Declaring a variable to hold file data in IGCSE Computer Science Paper 2

What it does: The variable LineOfText exists before READFILE stores a line of text in it. PlayerName tells the reader what the variable holds, and STRING matches text data. In 0478 pseudocode the form is DECLARE <identifier> : <data type>, with a colon between the name and the data type. DECLARE only creates the variable. OPENFILE is the command that opens the file.

Common mistakes: The colon is missing. A declaration needs the form DECLARE <identifier> : <data type>, so it should be DECLARE LineOfText : STRING. A declaration uses a colon between the identifier and the data type, not an equals sign. It should be DECLARE LineOfText : STRING.

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This module's key terms are also in a printable crossword (Modules 479–488) and word search (Modules 479–499).

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Learning

Duo

Which line correctly declares a variable to hold a line of text read from a file?

DECLARE LineOfText STRING =DECLARE LineOfText : STRING

Matches

READFILE "Notes.txt", LineOfText DECLARE LineOfText : STRING

↓

The variable is declared after READFILE uses it. DECLARE must come before the file command that uses the variable.

Applying

Meanings

Term

DECLARE LineOfText : STRING

Meaning

Creates a variable named LineOfText that holds text. Declare it before the file commands that use it, for example before READFILE stores a line in it.

Practice

DECLARE LineOfText : STRING

Testing

Gaps

LineOfText : STRING

Check Answer

Spots

1DECLARE LineOfText STRING

2OPENFILE "notes.txt" FOR READ

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Quick Questions

1. Which line correctly declares a variable to hold a line of text read from a file?

A. DECLARE LineOfText STRING =

B. DECLARE LineOfText : STRING ✓

In 0478 pseudocode the form is DECLARE <identifier> : <data type>, with a colon between the name and the data type.

2. Which line correctly declares a variable to hold a whole number, such as a score, that will be written to a file?

A. DECLARE Score : INTEGER ✓

B. DECLARE Score : STRING

A whole number is an INTEGER. STRING is for text, so it would be the wrong data type for a score.

3. When should DECLARE LineOfText : STRING appear in the program?

A. Before the READFILE command that stores a line in LineOfText ✓

B. After the READFILE command that stores a line in LineOfText

A variable must be declared before it is used. READFILE needs the variable to exist so it has somewhere to store the data.

4. Which identifier is the more meaningful choice for a variable that holds a line of text read from a file?

A. LineOfText ✓

B. x

A meaningful identifier shows what the variable holds, which makes the program easier to read and trace.

5. What does DECLARE do in a file handling program?

A. It opens the file so that data can be read from it

B. It creates a variable that can hold data read from or written to a file ✓

DECLARE only creates the variable. OPENFILE is the command that opens the file.

Match the Pairs

DECLARE LineOfText : STRING → Creates a variable called LineOfText that can hold a line of text read from or written to a file

DECLARE Score : INTEGER → Creates a variable called Score that can hold a whole number, such as a value read from a file

Declare the variable first, then use it to store a line read from the file → DECLARE LineOfText : STRING READFILE "Notes.txt", LineOfText

Give the variable a meaningful name and the correct data type for the file data → DECLARE PlayerName : STRING

READFILE "Notes.txt", LineOfText DECLARE LineOfText : STRING → The variable is declared after READFILE uses it. DECLARE must come before the file command that uses the variable.

DECLARE LineOfText STRING → The colon is missing between the identifier and the data type. It should be DECLARE LineOfText : STRING.

Key Term

DECLARE LineOfText : STRING

Creates a variable named LineOfText that holds text. Declare it before the file commands that use it, for example before READFILE stores a line in it.

Fill in the Blanks

1. DECLARE LineOfText : STRING

Hint: Type the keyword that creates a new variable before it is used.

2. DECLARE LineOfText : STRING

Hint: Type the data type used for variables that hold text.

3. DECLARE Score : INTEGER

Hint: Type the data type used for whole numbers.

4. DECLARE LineOfText : STRING OPENFILE "Notes.txt" FOR READ READFILE "Notes.txt", LineOfText

Hint: Type the name of the variable declared on the first line, which stores the line read from the file.

5. DECLARE Score : INTEGER OPENFILE "Scores.txt" FOR WRITE WRITEFILE "Scores.txt", Score

Hint: Type the variable name being declared, which must match the one written to the file on the last line.

Spot the Error

Question 1

A DECLARE LineOfText STRING

B OPENFILE "notes.txt" FOR READ

C READFILE "notes.txt", LineOfText

D CLOSEFILE "notes.txt"

Line A — The colon is missing. A declaration needs the form DECLARE <identifier> : <data type>, so it should be DECLARE LineOfText : STRING.

Question 2

A DECLARE Score : INTEGER

B DECLARE LineOfText = STRING

C OPENFILE "data.txt" FOR READ

D READFILE "data.txt", LineOfText

Line B — A declaration uses a colon between the identifier and the data type, not an equals sign. It should be DECLARE LineOfText : STRING.

Question 3

A DECLARE LineOfText : STRING

B OPENFILE "log.txt" FOR READ

C READFILE "log.txt", LineText

D CLOSEFILE "log.txt"

Line C — LineText was never declared. The variable that READFILE stores the data in must be the declared one, so it should be READFILE "log.txt", LineOfText.

Question 4

A DECLARE Score : INTEGER

B Score ← 50

C OPENFILE "score.txt" FOR WRTE

D WRITEFILE "score.txt", Score

E CLOSEFILE "score.txt"

Line C — WRTE is a spelling mistake. The file mode must be spelled WRITE, so it should be OPENFILE "score.txt" FOR WRITE.

Question 5

A DECLARE Name : STRING

B DECLARE Score : INTEGER

C Score ← "ten"

D Name ← "Ava"

Line C — Score was declared as INTEGER, so it cannot hold text. It should be assigned a whole number, such as Score ← 10.

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