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.