Basic formatting in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print a formatted integer using cout.

C++

#include <iostream>
int main() {
    int number = 42;
    std::cout << [1] << std::endl;
    return 0;
}

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

A"number"

Bstd::endl

Cnumber

D42

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around the variable name, which prints the word instead of the value.

Using std::endl instead of the variable.

The variable number holds the integer value to print. Using std::cout << number outputs its value.

2fill in blank

medium

Complete the code to print a floating-point number with two decimal places using std::fixed and std::setprecision.

C++

#include <iostream>
#include <iomanip>
int main() {
    double pi = 3.14159;
    std::cout << std::fixed << std::setprecision([1]) << pi << std::endl;
    return 0;
}

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

A3

B0

C1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using setprecision without std::fixed, which changes total digits instead of decimal places.

Choosing the wrong number for precision.

Using std::setprecision(2) with std::fixed formats the floating-point number to show two digits after the decimal point.

3fill in blank

hard

Fix the error in the code to print a string and an integer separated by a space.

C++

#include <iostream>
#include <string>
int main() {
    std::string name = "Alice";
    int age = 30;
    std::cout << name [1] " " << age << 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 + which tries to add strings and integers causing errors.

Using , which is not valid syntax for cout.

In C++, to print multiple items with std::cout, use the insertion operator << between each item.

4fill in blank

hard

Fill both blanks to create a formatted output that prints a number with a width of 5 and fills empty spaces with zeros.

C++

#include <iostream>
#include <iomanip>
int main() {
    int num = 7;
    std::cout << std::setw([1]) << std::setfill([2]) << num << std::endl;
    return 0;
}

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

A5

B'0'

C10

D' '

Attempts:

3 left

💡 Hint

Common Mistakes

Using a space character for fill instead of zero.

Setting width to a number other than 5.

std::setw(5) sets the width to 5 characters, and std::setfill('0') fills empty spaces with zeros.

5fill in blank

hard

Fill all three blanks to print a floating-point number with width 8, precision 3, and left alignment.

C++

#include <iostream>
#include <iomanip>
int main() {
    double value = 12.34567;
    std::cout << std::[1] << std::setw([2]) << std::setprecision([3]) << value << std::endl;
    return 0;
}

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

Aleft

B8

C3

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Using right alignment instead of left.

Mixing up width and precision values.

std::left aligns output to the left, std::setw(8) sets width to 8, and std::setprecision(3) sets decimal precision to 3.

Practice

1. What does the setw manipulator do in C++ output formatting?

easy

A. Sets the number of decimal places for floating numbers

B. Sets the width of the next output field

C. Changes the text color in the console

D. Aligns text to the center automatically

Solution

1. Step 1: Understand the purpose of setw

   The setw manipulator sets the width of the next output field in characters.

2. Step 2: Compare with other manipulators

   setprecision controls decimal places, not width. Color and alignment are not handled by setw.

3. Final Answer:

   Sets the width of the next output field -> Option B

4. Quick Check:

   setw = width setting [OK]

Hint: Remember: setw sets width, setprecision sets decimals [OK]

Common Mistakes:

• Confusing setw with setprecision
• Thinking setw changes text color
• Assuming setw aligns text automatically

2. Which of the following is the correct way to include setw in a C++ program?

easy

A. #include <string>

B. #include <format>

C. #include <iomanip>

D. #include <iostream>

Solution

1. Step 1: Identify the header for setw

   The setw manipulator is defined in the iomanip header.

2. Step 2: Check other headers

   iostream is for input/output streams but does not define setw. format and string are unrelated here.

3. Final Answer:

   #include <iomanip> -> Option C

4. Quick Check:

   setw needs iomanip header [OK]

Hint: Use <iomanip> for manipulators like setw [OK]

Common Mistakes:

• Including only <iostream> and expecting setw to work
• Confusing <format> with <iomanip>
• Forgetting to include any header for setw

3. What is the output of this code?

#include <iostream>
#include <iomanip>
using namespace std;

int main() {
  cout << setw(5) << 42 << endl;
  cout << setw(5) << 1234 << endl;
  return 0;
}

medium

A. 42
1234

B. 42
1234

C. 4321
24

D. 42
1234

Solution

1. Step 1: Understand setw effect on output

   setw(5) sets the width to 5 characters, padding with spaces on the left by default.

2. Step 2: Apply setw to numbers

   Number 42 is printed right-aligned in 5 spaces: 3 spaces + '42'. Number 1234 is 4 digits, so 1 space + '1234'.

3. Final Answer:

   42 1234 -> Option A

4. Quick Check:

   setw pads left with spaces [OK]

Hint: setw pads on left by default for numbers [OK]

Common Mistakes:

• Assuming setw pads on the right
• Ignoring spaces added by setw
• Thinking setw truncates numbers

4. Identify the error in this code snippet:

#include <iostream>
using namespace std;

int main() {
  cout << setw(10) << 3.14159 << endl;
  return 0;
}

medium

A. No error, code runs fine

B. Using cout without std:: prefix

C. Incorrect use of endl

D. Missing <iomanip> header for setw

Solution

1. Step 1: Check header includes

   The code uses setw but does not include <iomanip>, which is required.

2. Step 2: Verify other parts

   cout is used with using namespace std;, so no prefix needed. endl usage is correct.

3. Final Answer:

   Missing <iomanip> header for setw -> Option D

4. Quick Check:

   setw needs iomanip header [OK]

Hint: Always include <iomanip> when using setw [OK]

Common Mistakes:

• Forgetting to include <iomanip>
• Thinking cout needs std:: with using namespace std;
• Assuming endl usage causes error

5. How would you format the output of a floating-point number to always show exactly 3 decimal places and a total width of 8 characters, right-aligned?

hard

A. cout << fixed << setprecision(3) << setw(8) << number;

B. cout << setprecision(3) << setw(8) << number;

C. cout << setw(8) << fixed << number << setprecision(3);

D. cout << fixed << setw(3) << setprecision(8) << number;

Solution

1. Step 1: Set fixed decimal places

   Use fixed and setprecision(3) to show 3 decimals exactly.

2. Step 2: Set total width and alignment

   Use setw(8) to set total width to 8 characters, right-aligned by default.

3. Final Answer:

   cout << fixed << setprecision(3) << setw(8) << number; -> Option A

4. Quick Check:

   fixed + setprecision + setw(8) = correct format [OK]

Hint: Use fixed before setprecision, then setw for width [OK]

Common Mistakes:

• Omitting fixed causes variable decimals
• Placing setw before fixed and setprecision incorrectly
• Using wrong values for setw or setprecision