String input and output in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read a string from the user using std::cin.

C++

#include <iostream>
#include <string>

int main() {
    std::string name;
    std::cout << "Enter your name: ";
    std::cin [1] name;
    std::cout << "Hello, " << name << "!\n";
    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 >> with std::cin causes a compilation error.

Using == is a comparison operator, not for input.

The operator >> is used with std::cin to read input into a variable.

2fill in blank

medium

Complete the code to read a full line of text (including spaces) into a string variable.

C++

#include <iostream>
#include <string>

int main() {
    std::string sentence;
    std::cout << "Enter a sentence: ";
    std::getline(std::cin, [1]);
    std::cout << "You wrote: " << sentence << "\n";
    return 0;
}

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

Ainput

Bsentence

Cline

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a variable name that is not declared causes a compilation error.

Using std::cin >> variable reads only until the first space.

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

3fill in blank

hard

Fix the error in the code to correctly output the string variable message.

C++

#include <iostream>
#include <string>

int main() {
    std::string message = "Welcome!";
    std::cout [1] message [2] std::endl;
    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 << causes compilation errors.

Using + does not work with std::cout for output chaining.

To output text with std::cout, use the insertion operator <<.

4fill in blank

hard

Fill both blanks to create a dictionary (map) comprehension that stores word lengths for words longer than 3 characters.

C++

#include <iostream>
#include <string>
#include <map>
#include <vector>

int main() {
    std::vector<std::string> words = {"apple", "cat", "banana", "dog"};
    std::map<std::string, int> lengths;
    for (const auto& word : words) {
        if (word.[1]() > 3) {
            lengths[word] = word.[2]();
        }
    }
    for (const auto& [w, len] : lengths) {
        std::cout << w << ": " << len << "\n";
    }
    return 0;
}

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

Asize

Blength

Ccount

Dsize_t

Attempts:

3 left

💡 Hint

Common Mistakes

Using count() is incorrect because it does not exist for strings.

Using size_t is a type, not a method.

Use word.length() or word.size() to get the length of a string in C++. Both work, but here the first blank uses length() and the second uses size().

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths for words longer than 4 characters.

C++

#include <iostream>
#include <string>
#include <map>
#include <vector>
#include <algorithm>

int main() {
    std::vector<std::string> words = {"apple", "cat", "banana", "dog", "elephant"};
    std::map<std::string, int> result;
    for (auto word : words) {
        if (word.[1]() > 4) {
            std::transform(word.begin(), word.end(), word.begin(), ::[2]);
            result[[3]] = word.size();
        }
    }
    for (const auto& [w, len] : result) {
        std::cout << w << ": " << len << "\n";
    }
    return 0;
}

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

Alength

Btoupper

Cword

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using size() instead of length() in the condition is acceptable but here only length() is correct.

Using tolower instead of toupper changes to lowercase.

The code checks if the word length is greater than 4 using length(). It converts the word to uppercase using toupper in std::transform. Finally, it uses the uppercase word as the key in the map.

Practice

1. Which C++ statement correctly reads a full line of text including spaces into a string variable named name?

easy

A. std::cin >> name;

B. std::getline(std::cin, name);

C. std::cin.get(name);

D. getline(name, std::cin);

Solution

1. Step 1: Understand how to read full lines with spaces

   The function std::getline reads an entire line including spaces into a string.

2. Step 2: Identify correct syntax for reading from standard input

   The correct syntax is std::getline(std::cin, variable), so std::getline(std::cin, name); is correct.

3. Final Answer:

   std::getline(std::cin, name); -> Option B

4. Quick Check:

   Full line input = std::getline(std::cin, name) [OK]

Hint: Use std::getline to read full lines with spaces [OK]

Common Mistakes:

• Using std::cin >> name; reads only until first space
• Swapping arguments in getline function
• Using std::cin.get() incorrectly for strings

2. Which of the following is the correct way to print the string variable message to the console in C++?

easy

A. std::cout << message << std::endl;

B. print(message);

C. echo message;

D. console.log(message);

Solution

1. Step 1: Identify the standard output method in C++

   C++ uses std::cout to print output to the console.

2. Step 2: Use the insertion operator to print strings

   The correct syntax is std::cout << message << std::endl; to print the string and move to the next line.

3. Final Answer:

   std::cout << message << std::endl; -> Option A

4. Quick Check:

   Print string = std::cout << message << std::endl; [OK]

Hint: Use std::cout << variable << std::endl; to print strings [OK]

Common Mistakes:

• Using print() which is not a C++ function
• Using echo or console.log which are from other languages
• Forgetting std:: or << operator

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

std::string text;
std::getline(std::cin, text);
std::cout << "You entered: " << text << std::endl;

If the user inputs: Hello World

medium

A. You entered: Hello

B. You entered:

C. Compilation error

D. You entered: Hello World

Solution

1. Step 1: Understand std::getline input behavior

   std::getline(std::cin, text); reads the entire line including spaces, so it captures "Hello World".

2. Step 2: Output the stored string

   The output prints "You entered: " followed by the full input string, so it prints "You entered: Hello World".

3. Final Answer:

   You entered: Hello World -> Option D

4. Quick Check:

   getline reads full line = You entered: Hello World [OK]

Hint: std::getline reads full line including spaces [OK]

Common Mistakes:

• Assuming std::cin >> text reads full line
• Expecting only first word output
• Thinking code causes compilation error

4. Identify the error in this C++ code snippet that tries to read a string with spaces:

std::string input;
std::cin >> input;
std::cout << input << std::endl;

medium

A. std::string is not a valid type

B. Missing semicolon after std::string input

C. std::cin >> input; reads only until first space, not full line

D. std::cout cannot print strings directly

Solution

1. Step 1: Understand how std::cin >> works with strings

   std::cin >> input; reads input only until the first whitespace, so it cannot read full lines with spaces.

2. Step 2: Identify the correct method to read full lines

   To read full lines including spaces, std::getline(std::cin, input); should be used instead.

3. Final Answer:

   std::cin >> input; reads only until first space, not full line -> Option C

4. Quick Check:

   std::cin >> string reads until space [OK]

Hint: Use std::getline to read strings with spaces, not std::cin >> [OK]

Common Mistakes:

• Thinking std::cin >> reads full line
• Confusing syntax errors with input behavior
• Believing std::cout cannot print strings

5. You want to read a user's full name (which may contain spaces) and then print a greeting like Hello, [name]!. Which code snippet correctly does this in C++?

hard

A. std::string name;
std::getline(std::cin, name);
std::cout << "Hello, " << name << "!" << std::endl;

B. std::string name;
std::cin >> name;
std::cout << "Hello, " << name << "!" << std::endl;

C. char name[50];
std::cin >> name;
std::cout << "Hello, " << name << "!" << std::endl;

D. std::string name;
getline(name, std::cin);
std::cout << "Hello, " << name << "!" << std::endl;

Solution

1. Step 1: Choose method to read full name with spaces

   Using std::getline(std::cin, name); reads the entire line including spaces, perfect for full names.

2. Step 2: Print greeting with the name

   std::cout << "Hello, " << name << "!" << std::endl; correctly prints the greeting with the name.

3. Final Answer:

   std::string name; std::getline(std::cin, name); std::cout << "Hello, " << name << "!" << std::endl; -> Option A

4. Quick Check:

   Read full line + print greeting = std::string name; std::getline(std::cin, name); std::cout << "Hello, " << name << "!" << std::endl; [OK]

Hint: Use std::getline for full name input, then std::cout to print [OK]

Common Mistakes:

• Using std::cin >> which stops at first space
• Swapping arguments in getline function
• Using char arrays without proper input handling