← IGCSE Computer Science Paper 2

READFILE: reading a line of text

Reads the next line of text from the open file Names.txt into the STRING variable LineOfText. Each READFILE call reads the following line. Declare the variable first.

Part of: IGCSE Computer Science 0478 — 8.3 File Handling — Module 13

Understanding READFILE: reading a line of text in IGCSE Computer Science Paper 2

What it does: A line of text is a string, so the variable that receives it must be declared as STRING before READFILE uses it. The file keeps track of its position, so the second READFILE reads the line after the one read by the first.

Common mistakes: Quotes make OUTPUT display the words TextLine instead of the line read from the file. It should be OUTPUT TextLine, with no quotes, so the variable's contents are displayed. READFILE needs the file opened in READ mode. WRITE mode would replace the file's data with an empty file. It should be OPENFILE "Names.txt" FOR READ.

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This module's key terms are also in a printable crossword (Modules 489–499) and word search (Modules 479–499).

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Learning

Duo

Which statement reads one line of text from the open file Names.txt into a variable?

READFILE LineOfText, "Names.txt"READFILE "Names.txt", LineOfText

Matches

READFILE "Names.txt", "LineOfText"

↓

The variable name is in quotes, so it is a string literal and not a variable. It should be written without quotes: READFILE "Names.txt", LineOfText

Applying

Meanings

Term

READFILE "Names.txt", LineOfText

Meaning

Reads the next line of text from the open file Names.txt into the STRING variable LineOfText. Each READFILE call reads the following line. Declare the variable first.

Practice

DECLARE LineOfText : STRING

Testing

Gaps

"Names.txt", LineOfText

Check Answer

Spots

3READFILE "Names.txt", TextLine

4OUTPUT "TextLine"

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Quick Questions

1. Which statement reads one line of text from the open file Names.txt into a variable?

A. READFILE "Names.txt", LineOfText ✓

B. READFILE LineOfText, "Names.txt"

The file identifier comes first, then a comma, then the variable that receives the line.

2. Which declaration should come before READFILE "Names.txt", LineOfText to store a line of text?

A. DECLARE LineOfText : STRING ✓

B. DECLARE LineOfText : INTEGER

A whole line of text is stored in a STRING variable. An INTEGER variable can only hold whole numbers.

3. Names.txt is open for READ. READFILE "Names.txt", LineOfText runs twice in a row. What happens?

A. Both calls read line 1 of the file

B. The first call reads line 1 and the second call reads line 2 ✓

Each READFILE call moves on and reads the next line of the file.

4. Names.txt contains the lines Ava, Liam, Mia. After one READFILE "Names.txt", LineOfText, what does LineOfText hold?

A. Ava ✓

B. Ava, Liam, Mia

One READFILE reads only one line, so LineOfText holds just the first line, Ava.

5. Which line shows the line of text that was just read on the screen?

A. READFILE LineOfText

B. OUTPUT LineOfText ✓

READFILE only stores the line in the variable. OUTPUT is used to display it.

Match the Pairs

READFILE "Names.txt", LineOfText → Reads the next line of text from the open file Names.txt and stores it in the variable LineOfText

OUTPUT LineOfText → Displays the line of text that READFILE has just stored in the variable

Declare the STRING variable first so it can hold a line of text read from the file → DECLARE LineOfText : STRING

Each READFILE call reads the next line, so two calls in a row read the first and then the second line → READFILE "Names.txt", LineOfText READFILE "Names.txt", LineOfText

READFILE "Names.txt", "LineOfText" → The variable name is in quotes, so it is a string literal and not a variable. It should be written without quotes: READFILE "Names.txt", LineOfText

DECLARE LineOfText : INTEGER READFILE "Names.txt", LineOfText → LineOfText is declared as INTEGER but a line of text must be stored in a STRING variable. It should be DECLARE LineOfText : STRING

Key Term

READFILE "Names.txt", LineOfText

Reads the next line of text from the open file Names.txt into the STRING variable LineOfText. Each READFILE call reads the following line. Declare the variable first.

Fill in the Blanks

1. READFILE "Names.txt", LineOfText

Hint: Type the keyword that reads the next line from an open file.

2. DECLARE LineOfText : STRING READFILE "Names.txt", LineOfText

Hint: Type the data type that holds a line of text.

3. READFILE "Names.txt", LineOfText OUTPUT LineOfText

Hint: Type the variable that receives the line read from the file.

4. READFILE "Names.txt", LineOfText OUTPUT LineOfText

Hint: Type the keyword that displays the line on the screen.

5. OPENFILE "Names.txt" FOR READ READFILE "Names.txt", LineOfText OUTPUT LineOfText

Hint: Type the file mode needed before lines can be read from the file.

Spot the Error

Question 1

A DECLARE TextLine : STRING

B OPENFILE "Names.txt" FOR READ

C READFILE "Names.txt", TextLine

D OUTPUT "TextLine"

E CLOSEFILE "Names.txt"

Line D — Quotes make OUTPUT display the words TextLine instead of the line read from the file. It should be OUTPUT TextLine, with no quotes, so the variable's contents are displayed.

Question 2

A DECLARE TextLine : STRING

B OPENFILE "Names.txt" FOR WRITE

C READFILE "Names.txt", TextLine

D OUTPUT TextLine

Line B — READFILE needs the file opened in READ mode. WRITE mode would replace the file's data with an empty file. It should be OPENFILE "Names.txt" FOR READ.

Question 3

A DECLARE TextLine : STRING

B OPENFILE "Names.txt" READ

C READFILE "Names.txt", TextLine

D OUTPUT TextLine

E CLOSEFILE "Names.txt"

Line B — The keyword FOR is missing. The correct syntax is OPENFILE "Names.txt" FOR READ.

Question 4

A DECLARE TextLine : STRING

B OPENFILE "Names.txt" FOR READ

C READFILE "Names.txt" TextLine

D OUTPUT TextLine

E READFILE "Names.txt", TextLine

F OUTPUT TextLine

Line C — A comma is missing between the file name and the variable. It should be READFILE "Names.txt", TextLine.

Question 5

A DECLARE TextLine : INTEGER

B OPENFILE "Names.txt" FOR READ

C READFILE "Names.txt", TextLine

D OUTPUT TextLine

Line A — A line of text must be stored in a STRING variable. An INTEGER variable cannot hold text. It should be DECLARE TextLine : STRING.

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