← IGCSE Computer Science Paper 2

File modes: READ and WRITE

States what a program will do with an open file: READ gets data out of it, WRITE puts data into it. A file is open in only one mode at a time, chosen by what the program needs.

Part of: IGCSE Computer Science 0478 — 8.3 File Handling — Module 3

Understanding File modes: READ and WRITE in IGCSE Computer Science Paper 2

What it does: Getting data out of a file needs READ mode, so FOR READ is written after the file name. In 0478 pseudocode a file is opened in one mode only. To change what you do with it, close it and open it again in the other mode.

Common mistakes: The file was opened FOR READ, so the program can only read from it. It must use READFILE "names.txt", Name to get data out. WRITEFILE needs the file to be open FOR WRITE. The program wants to put Score into the file with WRITEFILE, so the file must be opened FOR WRITE. FOR READ only lets the program get data out of the file.

Class: _____________________ · Name: _____________________ · Date: _________

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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

A program must load saved high scores from a file. Which mode should it use?

READWRITE

Matches

OPENFILE "data.txt" FOR READ WRITEFILE "data.txt", Score

↓

The file is open in READ mode, but the program tries to write data to it. A file opened FOR READ can only be read.

Applying

Meanings

Term

file mode

Meaning

States what a program will do with an open file: READ gets data out of it, WRITE puts data into it. A file is open in only one mode at a time, chosen by what the program needs.

Practice

OPENFILE "Scores.txt" FOR WRITE

Testing

Gaps

OPENFILE "marks.txt" FOR

Check Answer

Spots

2OPENFILE "names.txt" FOR READ

3WRITEFILE "names.txt", Name

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Quick Questions

1. A program must load saved high scores from a file. Which mode should it use?

A. READ ✓

B. WRITE

READ gets data out of a file, so use it when the program needs to load data that is already saved.

2. A program must save a player's name into a file. Which mode should it use?

A. READ

B. WRITE ✓

WRITE puts data into a file, so use it when the program needs to save data.

3. Which line opens a file so data can be put into it?

A. OPENFILE "Scores.txt" FOR WRITE ✓

B. OPENFILE "Scores.txt" FOR READ

FOR WRITE means data will be written to the file. FOR READ would only let the program get data out.

4. Which statement about file modes is true?

A. A file mode states what the file is called

B. A file mode states what the program will do with the open file ✓

The mode (READ or WRITE) describes the action the program will take. The file name is the file identifier, a separate idea.

5. Which statement about modes is true?

A. A file is open in only one mode at a time ✓

B. A file can be open in READ and WRITE mode at the same time

In 0478 pseudocode a file is opened in one mode only. To change what you do with it, close it and open it again in the other mode.

Match the Pairs

OPENFILE "scores.txt" FOR READ → Opens the file in READ mode so the program can get data out of it

OPENFILE "scores.txt" FOR WRITE → Opens the file in WRITE mode so the program can put data into it

The program needs to get saved data out of a file, so it chooses READ mode → OPENFILE "names.txt" FOR READ

The program needs to save a new high score into a file, so it chooses WRITE mode → OPENFILE "best.txt" FOR WRITE

OPENFILE "data.txt" FOR READ WRITEFILE "data.txt", Score → The file is open in READ mode, but the program tries to write data to it. A file opened FOR READ can only be read.

OPENFILE "data.txt" FOR WRITE READFILE "data.txt", Score → The file is open in WRITE mode, but the program tries to read data from it. A file opened FOR WRITE can only be written to.

Key Term

file mode

States what a program will do with an open file: READ gets data out of it, WRITE puts data into it. A file is open in only one mode at a time, chosen by what the program needs.

Fill in the Blanks

1. OPENFILE "marks.txt" FOR WRITE WRITEFILE "marks.txt", Score CLOSEFILE "marks.txt"

Hint: Type the file mode used when the program puts data into a file.

2. OPENFILE "names.txt" FOR READ READFILE "names.txt", Name CLOSEFILE "names.txt"

Hint: Type the file mode used when the program gets data out of a file.

3. OPENFILE "log.txt" FOR READ READFILE "log.txt", Entry CLOSEFILE "log.txt"

Hint: Type the keyword that comes before the file mode in an open statement.

4. OPENFILE "data.txt" FOR READ READFILE "data.txt", Item CLOSEFILE "data.txt"

Hint: Type the command that opens a file and states its mode.

5. // Load the saved score OPENFILE "best.txt" FOR READ READFILE "best.txt", HighScore

Hint: Choose the mode that matches the comment: the program needs to get data out of the file.

Spot the Error

Question 1

A DECLARE Name : STRING

B OPENFILE "names.txt" FOR READ

C WRITEFILE "names.txt", Name

D CLOSEFILE "names.txt"

Line C — The file was opened FOR READ, so the program can only read from it. It must use READFILE "names.txt", Name to get data out. WRITEFILE needs the file to be open FOR WRITE.

Question 2

A DECLARE Score : INTEGER

B OPENFILE "data.txt" FOR READ

C WRITEFILE "data.txt", Score

D CLOSEFILE "data.txt"

Line B — The program wants to put Score into the file with WRITEFILE, so the file must be opened FOR WRITE. FOR READ only lets the program get data out of the file.

Question 3

A OPENFILE "pets.txt" FOR WRITE

B WRITEFILE "pets.txt", "Cat"

C READFILE "pets.txt", Pet

D CLOSEFILE "pets.txt"

Line C — The file is open in WRITE mode, so the program cannot read from it. Line 3 should be WRITEFILE "pets.txt", "Dog" to put the next item into the file.

Question 4

A OPENFILE "a.txt" FOR READ

B READFILE "a.txt", Line

C OPENFILE "a.txt" FOR WRITE

D OPENFILE "a.txt" FOR WRITE

E WRITEFILE "a.txt", Line

Line C — A file is open in only one mode at a time. The READ file must be closed with CLOSEFILE "a.txt" before it is opened again FOR WRITE on line 4.

Question 5

A DECLARE Total : INTEGER

B OPENFILE "total.txt" READ

C READFILE "total.txt", Total

D OUTPUT Total

Line B — The file mode must be introduced with the keyword FOR. The correct line is OPENFILE "total.txt" FOR READ.

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