Using cout for output in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, World!" using cout.

C++

#include <iostream>
int main() {
    std::[1] << "Hello, World!" << std::endl;
    return 0;
}

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

Acerr

Bcin

Ccout

Dclog

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cin' instead of 'cout' for output.

Using 'cerr' which is for error output, not normal output.

The cout object is used to output text to the console in C++.

2fill in blank

medium

Complete the code to print the value of variable x using cout.

C++

#include <iostream>
int main() {
    int x = 5;
    std::cout << "Value: " << [1] << std::endl;
    return 0;
}

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

Astd::endl

B"x"

C5

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the variable name in quotes, which prints the text instead of the value.

Using a number directly instead of the variable.

To print the value of a variable, use its name without quotes.

3fill in blank

hard

Fix the error in the code to correctly print "Sum: 15" using cout.

C++

#include <iostream>
int main() {
    int a = 7, b = 8;
    std::cout << "Sum: " [1] a + b << 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 '<<' between string and variables.

Using '>>' which is for input, not output.

The insertion operator << is needed to send multiple parts to cout.

4fill in blank

hard

Fill both blanks to print the product of a and b with a message.

C++

#include <iostream>
int main() {
    int a = 4, b = 6;
    std::cout [1] "Product: " [2] a * b << 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 '+' or '*' operators instead of '<<' for output chaining.

Using '>>' which is for input.

Use the insertion operator << to send both the string and the product to cout.

5fill in blank

hard

Fill all three blanks to print the sum and difference of x and y.

C++

#include <iostream>
int main() {
    int x = 10, y = 3;
    std::cout [1] "Sum: " [2] x + y << ", Difference: " [3] x - y << std::endl;
    return 0;
}

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

A<<

B+

D>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '<<' for output chaining.

Using '>>' which is for input.

Not adding numbers correctly.

Use << to send strings and results to cout.

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