Basic formatting in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of std::cout in C++?

std::cout is used to print output to the console (screen). It helps us show messages or results to the user.

beginner

How do you print a new line in C++ using std::cout?

You can print a new line by using \n inside the string or by using std::endl after the output.

beginner

What does this code print?

std::cout << "Hello" << " " << "World!" << std::endl;

This prints: Hello World! followed by a new line.

intermediate

What is the difference between \n and std::endl in C++ output?

\n adds a new line character but does not flush the output buffer immediately.
std::endl adds a new line and also flushes the output buffer, making sure output appears right away.

beginner

How can you print variables with text in C++ using std::cout?

You can use the insertion operator << to combine text and variables. For example:
int age = 25;
std::cout << "Age: " << age << std::endl;

Which of these prints a new line in C++?

A std::cout << "\n";

B std::cout << "newline";

C std::cout << "\t";

D std::cout << "space";

\n is the new line character. It moves the cursor to the next line.

What does std::endl do besides adding a new line?

A Adds a tab space

B Flushes the output buffer

C Ends the program

D Starts a new program

std::endl adds a new line and flushes the output buffer to show output immediately.

How do you print the value of an integer variable num with text?

A std::cout << "Number: " << num << std::endl;

B print("Number: " + num);

C echo "Number: " num;

D cout << num + "Number";

Use std::cout with << to combine text and variables.

What symbol is used to send output to the console in C++?

A ==

B >>

C <<

D //

The insertion operator << sends data to std::cout for output.

Which line correctly prints "Hello World!" followed by a new line?

A print("Hello World!\n");

B std::cout >> "Hello World!";

C echo "Hello World!";

D std::cout << "Hello World!" << std::endl;

Option D uses correct C++ syntax for printing with a new line.

Explain how to print text and variables together in C++ using std::cout.

Think about how you join strings and numbers in one output line.

Describe the difference between using \n and std::endl for new lines in C++ output.

Consider what happens behind the scenes when output is shown.

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