String input and output in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of string input with getline and cin

What is the output of this C++ code when the input is:

John Doe

C++

#include <iostream>
#include <string>

int main() {
    std::string firstName, lastName;
    std::cin >> firstName;
    std::getline(std::cin, lastName);
    std::cout << "First: " << firstName << ", Last:" << lastName << std::endl;
    return 0;
}

A First: John Doe, Last:

B First: John, Last: Doe

C First: John, Last:

D First: John, Last: Doe

💡 Hint

Remember that std::cin >> reads until space, getline reads until newline including leading spaces.

The std::cin >> firstName reads 'John' stopping at space. getline reads the rest of the line including the leading space before 'Doe'. So lastName contains ' Doe' with a leading space.

❓ Predict Output

intermediate

Output of string concatenation and output formatting

What is the output of this C++ code?

C++

#include <iostream>
#include <string>

int main() {
    std::string s1 = "Hello";
    std::string s2 = "World";
    std::cout << s1 + ", " + s2 + "!" << std::endl;
    return 0;
}

A Hello,World!

B HelloWorld!

C Hello World!

D Hello, World!

💡 Hint

Look carefully at the commas and spaces in the concatenation.

The code concatenates s1, then a comma and space, then s2, then an exclamation mark. So the output is 'Hello, World!'.

❓ Predict Output

advanced

Output of reading multiple words with getline and cin

What is the output of this code if the input is:

Mary Jane Watson

C++

#include <iostream>
#include <string>

int main() {
    std::string first, last;
    std::getline(std::cin, first, ' ');
    std::getline(std::cin, last);
    std::cout << "First: " << first << ", Last: " << last << std::endl;
    return 0;
}

A First: Mary, Last: Jane Watson

B First: Mary Jane, Last: Watson

C First: Mary, Last: Jane

D First: Mary Jane Watson, Last:

💡 Hint

getline with a delimiter reads until that delimiter, not the whole line.

The first getline reads until the first space, so first = 'Mary'. The second getline reads the rest of the line, so last = 'Jane Watson'.

❓ Predict Output

advanced

Output of mixing cin and getline with leftover newline

What is the output of this code if the input is:

42
Hello World

C++

#include <iostream>
#include <string>

int main() {
    int number;
    std::string text;
    std::cin >> number;
    std::getline(std::cin, text);
    std::cout << "Number: " << number << ", Text: '" << text << "'" << std::endl;
    return 0;
}

A Number: 42, Text: ''

B Number: 42, Text: ' Hello World'

C Number: 42, Text: 'Hello World'

D Number: 42, Text: '\nHello World'

💡 Hint

After reading number with >>, the newline remains in the input buffer.

std::cin >> number reads 42 but leaves the newline. getline reads until newline, so it reads an empty string. So text is empty.

🧠 Conceptual

expert

Why does mixing cin >> and getline cause issues?

Why does mixing std::cin >> and std::getline often cause unexpected empty string inputs?

A Because std::cin >> converts input to uppercase, confusing getline.

B Because std::getline cannot read strings after std::cin >> is used once.

C Because std::cin >> leaves the newline character in the input buffer, which std::getline reads as an empty line.

D Because std::getline automatically skips whitespace, causing it to miss input.

💡 Hint

Think about what happens to the newline character after std::cin >> reads input.

std::cin >> reads input but stops before newline, leaving it in the buffer. std::getline reads until newline, so it reads the leftover newline as an empty string.

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