Reading and writing files in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file for writing.

C++

#include <fstream>

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

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

Aclose

Bwrite

Copen

Dread

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'read' instead of 'open' to open the file.

Trying to write before opening the file.

The open function is used to open a file stream in C++.

2fill in blank

medium

Complete the code to read a line from a file.

C++

#include <fstream>
#include <string>
#include <iostream>

int main() {
    std::ifstream file("input.txt");
    std::string line;
    if (std::getline(file, [1])) {
        std::cout << line << std::endl;
    }
    file.close();
    return 0;
}

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

Aline

Bfile

Ctext

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the file stream instead of the string variable.

Using an undeclared variable.

The std::getline function reads a line into the variable passed as the second argument, here line.

3fill in blank

hard

Fix the error in the code to write numbers to a file.

C++

#include <fstream>

int main() {
    std::ofstream file("numbers.txt");
    for (int i = 1; i <= 5; i++) {
        file << i [1] " ";
    }
    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 '+' which tries to add instead of writing.

Using '>>' which is for input streams.

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

4fill in blank

hard

Fill both blanks to create a map of word lengths from a file.

C++

#include <fstream>
#include <string>
#include <map>

int main() {
    std::ifstream file("words.txt");
    std::map<std::string, int> wordLengths;
    std::string word;
    while (file >> [1]) {
        wordLengths[[2]] = word.length();
    }
    file.close();
    return 0;
}

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

Aword

Bfile

Clength

Dline

Attempts:

3 left

💡 Hint

Common Mistakes

Using the file stream as a key instead of the word.

Using an undefined variable.

The variable word is used to read each word and as the key in the map.

5fill in blank

hard

Fill all three blanks to write only words longer than 3 characters to a file.

C++

#include <fstream>
#include <string>
#include <vector>

int main() {
    std::vector<std::string> words = {"cat", "house", "dog", "elephant"};
    std::ofstream file("long_words.txt");
    for (const auto& [1] : words) {
        if ([2].length() [3] 3) {
            file << word << std::endl;
        }
    }
    file.close();
    return 0;
}

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

Aword

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the loop and condition.

Using '<' instead of '>' in the condition.

The loop variable is word. We check if word.length() is greater than 3 to write it.