Why file handling is required in C++ - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file for reading.

C++

#include <fstream>
int main() {
    std::ifstream file[1];
    return 0;
}

Drag options to blanks, or click blank then click option'

A("data.txt")

B["data.txt"]

C{data.txt}

D<data.txt>

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets or braces instead of parentheses.

Not passing the filename as a string.

To open a file in C++, you use parentheses with the filename as a string.

2fill in blank

medium

Complete the code to write text to a file.

C++

#include <fstream>
int main() {
    std::ofstream file("output.txt");
    file[1] "Hello, file!";
    file.close();
    return 0;
}

Drag options to blanks, or click blank then click option'

A+=

B>>

C<<

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using >> instead of << for writing.

Using assignment operator = which is invalid here.

To write to a file stream, use the insertion operator <<.

3fill in blank

hard

Fix the error in the code to read a line from a file.

C++

#include <fstream>
#include <string>
int main() {
    std::ifstream file("input.txt");
    std::string line;
    if (file.is_open()) {
        std::getline(file[1], line);
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

A)

B(

C;

D]

Attempts:

3 left

💡 Hint

Common Mistakes

Missing closing parenthesis.

Using brackets or semicolon instead of closing parenthesis.

The getline function requires the file stream as the first argument inside parentheses.

4fill in blank

hard

Fill both blanks to create a file and write multiple lines.

C++

#include <fstream>
int main() {
    std::ofstream file[1];
    file << "Line 1" << std::endl[2];
    file.close();
    return 0;
}

Drag options to blanks, or click blank then click option'

A("log.txt")

B("data.txt")

C<<

D>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong filename or wrong operator for writing.

Using >> instead of << for writing.

Use parentheses with filename to open file and << operator to write lines.

5fill in blank

hard

Fill both blanks to read from a file and print its content.

C++

#include <fstream>
#include <iostream>
#include <string>
int main() {
    std::ifstream file[1];
    std::string line;
    while (std::getline(file, line)) {
        std::cout[2] line << std::endl;;
    }
    file.close();
    return 0;
}

Drag options to blanks, or click blank then click option'

A("readme.txt")

B<<

C;

D>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using >> instead of << for output.

Missing semicolon at the end of the output statement.

Open file with filename in parentheses, use << to print, and end statement with semicolon.

Practice

1. Why is file handling required in C++ programming?

easy

A. To save data permanently and retrieve it later

B. To make the program run faster

C. To display graphics on the screen

D. To create user interfaces

Solution

1. Step 1: Understand the purpose of file handling

   File handling allows programs to save data to files so it is not lost when the program ends.

2. Step 2: Identify the correct use case

   Saving data permanently and retrieving it later is the main reason for file handling, unlike graphics or speed improvements.

3. Final Answer:

   To save data permanently and retrieve it later -> Option A

4. Quick Check:

   File handling = permanent data storage [OK]

Hint: File handling = saving and loading data files [OK]

Common Mistakes:

• Confusing file handling with graphics or UI
• Thinking file handling speeds up program execution
• Assuming file handling is only for temporary data

2. Which of the following is the correct way to include the file handling library in C++?

easy

A. #include <iostream>

B. #include <string>

C. #include <fstream>

D. #include <vector>

Solution

1. Step 1: Recall the library for file handling

   The fstream library is used in C++ for file input and output operations.

2. Step 2: Match the correct include statement

   Only #include <fstream> provides file handling capabilities, others are for different purposes.

3. Final Answer:

   #include <fstream> -> Option C

4. Quick Check:

   File handling library = fstream [OK]

Hint: File handling needs fstream library included [OK]

Common Mistakes:

• Including iostream instead of fstream
• Confusing string or vector libraries with file handling
• Forgetting to include any library

3. What will be the output of the following C++ code?

#include <fstream>
#include <iostream>
using namespace std;

int main() {
  ofstream file("data.txt");
  file << "Hello World";
  file.close();
  ifstream readFile("data.txt");
  string content;
  readFile >> content;
  cout << content;
  return 0;
}

medium

A. Compilation error

B. Hello World

C. World

D. Hello

Solution

1. Step 1: Analyze file writing

   The program writes "Hello World" to the file data.txt using ofstream.

2. Step 2: Analyze file reading

   When reading with >> operator, it reads only up to the first whitespace, so it reads "Hello" only.

3. Final Answer:

   Hello -> Option D

4. Quick Check:

   Reading with >> stops at space = Hello [OK]

Hint: >> reads only until first space in file [OK]

Common Mistakes:

• Expecting full line output with >> operator
• Assuming file content is printed directly without reading
• Thinking code causes compilation error

4. Identify the error in the following C++ code snippet related to file handling:

#include <fstream>
#include <string>
using namespace std;

int main() {
  ifstream file;
  file.open("info.txt");
  string data;
  file >> data;
  cout << data;
  return 0;
}

medium

A. Using ifstream instead of ofstream

B. Missing #include <iostream> for cout

C. File not opened before reading

D. No error in the code

Solution

1. Step 1: Check included libraries

   The code uses cout but does not include <iostream>, which is required for input/output streams.

2. Step 2: Verify file opening and reading

   The file is opened correctly with ifstream and read properly, so no error there.

3. Final Answer:

   Missing #include <iostream> for cout -> Option B

4. Quick Check:

   cout needs iostream included [OK]

Hint: Always include iostream when using cout [OK]

Common Mistakes:

• Ignoring missing iostream include
• Thinking file not opened is the error
• Confusing ifstream and ofstream usage

5. You want to save user settings in a file and load them when the program starts. Which approach best uses file handling in C++?

hard

A. Use ofstream to write settings to a file and ifstream to read them back

B. Store settings only in variables without files

C. Use cout to display settings on screen

D. Use cin to input settings every time program runs

Solution

1. Step 1: Understand saving and loading data

   To keep user settings between program runs, data must be saved to and read from a file.

2. Step 2: Identify correct file handling classes

   ofstream writes data to files, and ifstream reads data from files, making them suitable for this task.

3. Final Answer:

   Use ofstream to write settings to a file and ifstream to read them back -> Option A

4. Quick Check:

   Save/load settings = ofstream + ifstream [OK]

Hint: Write with ofstream, read with ifstream for persistent data [OK]

Common Mistakes:

• Not saving settings to a file
• Using console input/output instead of files
• Assuming variables keep data after program ends