Using cout for output in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained cout statements

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    std::cout << "Hello" << ", " << "World!" << std::endl;
    return 0;
}

A Hello, World!\n

B Hello World!\n

C Hello,World!\n

D Hello\n, \nWorld!\n

💡 Hint

Look at how the strings and commas are chained with << operators.

The code prints the strings exactly as chained with <<, so it outputs 'Hello, World!' followed by a newline.

❓ Predict Output

intermediate

Output with multiple cout lines

What will be printed when this code runs?

C++

#include <iostream>
int main() {
    std::cout << "Line 1" << std::endl;
    std::cout << "Line 2";
    std::cout << " Line 3" << std::endl;
    return 0;
}

A Line 1\nLine 2 Line 3\n

B Line 1\nLine 2 Line 3

C Line 1\nLine 2\nLine 3\n

D Line 1 Line 2 Line 3\n

💡 Hint

Check where std::endl is used to add new lines.

The first cout ends with std::endl adding a newline. The second cout prints without newline, so the third cout continues on the same line and ends with std::endl.

❓ Predict Output

advanced

Output with mixed data types using cout

What is the output of this code snippet?

C++

#include <iostream>
int main() {
    int a = 5;
    double b = 3.2;
    std::cout << "a = " << a << ", b = " << b << std::endl;
    return 0;
}

A a = 5 b = 3.2\n

B a = 5, b = 3.2\n

C a = 5, b = 3.200000\n

D a = 5, b = 3.20\n

💡 Hint

By default, double prints with minimal decimals unless formatted.

The double value prints as 3.2 by default without extra trailing zeros.

❓ Predict Output

advanced

Output with cout and escape sequences

What will this program print?

C++

#include <iostream>
int main() {
    std::cout << "First Line\nSecond Line\tTabbed" << std::endl;
    return 0;
}

A

First Line\nSecond Line Tabbed

B First Line\nSecond Line\tTabbed\n

C

First Line Second Line Tabbed

D

First Line
Second Line	Tabbed

💡 Hint

Escape sequences like \n and \t create new lines and tabs in output.

The \n creates a new line and \t adds a tab space in the output.

❓ Predict Output

expert

Output of cout with pointer and address

What is the output of this code?

C++

#include <iostream>
int main() {
    int x = 10;
    int* p = &x;
    std::cout << "Value: " << *p << ", Address: " << p << std::endl;
    return 0;
}

A Value: 10, Address: *p\n

B Value: 10 Address: 0x7ffee3bff6ac\n

C Value: 10, Address: 0x7ffee3bff6ac\n

D Value: 10, Address: 10\n

💡 Hint

The pointer prints the memory address, which looks like a hex number starting with 0x.

The *p dereferences the pointer to print the value 10, and p prints the memory address in hexadecimal format.

Practice

1. What does the following C++ code do?
std::cout << "Hello, world!" << std::endl;

easy

A. Creates a variable named 'Hello, world!'

B. Reads input from the user

C. Saves 'Hello, world!' to a file

D. Prints 'Hello, world!' followed by a new line on the screen

Solution

1. Step 1: Understand the use of std::cout

   std::cout is used to print output to the screen.

2. Step 2: Analyze the code line

   The code sends the string "Hello, world!" to std::cout and then adds a new line with std::endl.

3. Final Answer:

   Prints 'Hello, world!' followed by a new line on the screen -> Option D

4. Quick Check:

   cout prints text + endl adds new line = A [OK]

Hint: cout prints text; endl adds a new line [OK]

Common Mistakes:

• Thinking cout reads input
• Confusing cout with file operations
• Missing std:: before cout or endl

2. Which of the following is the correct syntax to print the number 10 using cout?

easy

A. cout << 10 << end;

B. cout >> 10 >> endl;

C. std::cout << 10 << std::endl;

D. std::cout << "10" >> std::endl;

Solution

1. Step 1: Identify correct insertion operator

   The operator to send data to cout is <<, not >>.

2. Step 2: Check for correct use of std::endl

   The correct manipulator to end the line is std::endl, not end.

3. Final Answer:

   std::cout << 10 << std::endl; -> Option C

4. Quick Check:

   Use << and std::endl for output [OK]

Hint: Use << to send data to cout and std::endl to end line [OK]

Common Mistakes:

• Using >> instead of <<
• Forgetting std:: before cout or endl
• Typing end instead of std::endl

3. What is the output of the following code?

#include <iostream>
int main() {
  std::cout << "Sum: " << 5 + 3 << std::endl;
  return 0;
}

medium

A. Sum: 53

B. Sum: 8

C. 8

D. Sum:

Solution

1. Step 1: Understand operator precedence in cout

   The expression 5 + 3 is evaluated first because + has higher precedence than <<.

2. Step 2: Combine the string and sum

   The string "Sum: " is printed, then the result 8, then a new line.

3. Final Answer:

   Sum: 8 -> Option B

4. Quick Check:

   5+3=8, printed after 'Sum: ' [OK]

Hint: Remember + evaluates before << in cout [OK]

Common Mistakes:

• Thinking cout concatenates numbers as strings
• Reading output as 'Sum: 53'
• Ignoring operator precedence

4. Find the error in this code snippet:

#include <iostream>
int main() {
  std::cout << "Hello" << std::endl
  return 0;
}

medium

A. Missing semicolon after std::endl

B. Wrong operator used instead of <<

C. std::cout should be cout only

D. Missing #include <string>

Solution

1. Step 1: Check line endings

   Every statement in C++ must end with a semicolon. The line with std::endl is missing it.

2. Step 2: Verify other syntax

   The operators and includes are correct; only the semicolon is missing.

3. Final Answer:

   Missing semicolon after std::endl -> Option A

4. Quick Check:

   Statements end with ; in C++ [OK]

Hint: Check for missing semicolons after cout lines [OK]

Common Mistakes:

• Forgetting semicolon at end of statement
• Confusing << with >>
• Removing std:: prefix incorrectly

5. You want to print multiple variables on one line separated by spaces. Which code correctly prints int a = 5; and int b = 10; as "5 10" using cout?

hard

A. std::cout << a << " " << b << std::endl;

B. std::cout << a + " " + b << std::endl;

C. std::cout << a, " ", b << std::endl;

D. std::cout << a << b << std::endl;

Solution

1. Step 1: Understand how to print multiple items with spaces

   Use << to send each item separately, including a string with a space.

2. Step 2: Check each option

   std::cout << a << " " << b << std::endl; correctly sends a, then a space string, then b, then ends the line.

3. Final Answer:

   std::cout << a << " " << b << std::endl; -> Option A

4. Quick Check:

   Use << between variables and strings for spaces [OK]

Hint: Use << between variables and " " for spaces [OK]

Common Mistakes:

• Trying to add int and string with +
• Using commas instead of <<
• Printing variables without spaces