Basic formatting in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of formatted floating-point number

What is the output of this C++ code snippet?

C++

#include <iostream>
#include <iomanip>

int main() {
    double pi = 3.1415926535;
    std::cout << std::fixed << std::setprecision(3) << pi << std::endl;
    return 0;
}

A 3.1416

B 3.14159

C 3.141

D 3.142

💡 Hint

Look at how many digits are shown after the decimal point with setprecision.

std::fixed with std::setprecision(3) formats the number to show exactly 3 digits after the decimal point, rounding the value. 3.1415926535 rounded to 3 decimals is 3.142.

❓ Predict Output

intermediate

Output of formatted integer with width and fill

What is the output of this C++ code?

C++

#include <iostream>
#include <iomanip>

int main() {
    int num = 42;
    std::cout << std::setw(5) << std::setfill('0') << num << std::endl;
    return 0;
}

A 00042

B 0042

C 43

D 42

💡 Hint

setw sets the total width, setfill sets the padding character.

setw(5) sets the total width to 5 characters. setfill('0') fills empty spaces with zeros on the left by default. So 42 becomes 00042.

❓ Predict Output

advanced

Output of mixed formatting flags

What is the output of this C++ code snippet?

C++

#include <iostream>
#include <iomanip>

int main() {
    int num = 255;
    std::cout << std::hex << std::uppercase << std::setw(6) << std::setfill('*') << num << std::endl;
    return 0;
}

A ****FF

B ***FF

C ***0FF

D FF0***

💡 Hint

hex converts to base 16, uppercase makes letters capital, setw and setfill control width and fill.

255 in hex is FF. setw(6) means total width 6, setfill('*') fills with '*'. The output is ****FF because the number is right aligned and the fill fills the left side.

❓ Predict Output

advanced

Output of left and right alignment with width

What is the output of this C++ code?

C++

#include <iostream>
#include <iomanip>

int main() {
    std::cout << std::left << std::setw(6) << 123 << "X" << std::endl;
    std::cout << std::right << std::setw(6) << 123 << "X" << std::endl;
    return 0;
}

A

   123X
123   X

B

123   X
   123X

C

123X
123X

D

123   X
123   X

💡 Hint

left aligns text, right aligns text, setw sets width.

First line uses std::left with setw(6), so 123 is printed left aligned in 6 spaces, then X. Second line uses std::right with setw(6), so 123 is right aligned in 6 spaces, then X.

🧠 Conceptual

expert

Effect of std::boolalpha on boolean output

Which option shows the output of this C++ code?

C++

#include <iostream>

int main() {
    bool flag = true;
    std::cout << std::boolalpha << flag << std::endl;
    std::cout << std::noboolalpha << flag << std::endl;
    return 0;
}

A

1
1

B

1
true

C

true
1

D

true
true

💡 Hint

std::boolalpha prints true/false, std::noboolalpha prints 1/0.

std::boolalpha causes bool values to print as 'true' or 'false'. std::noboolalpha resets this, so bool prints as 1 or 0. So first line prints 'true', second line prints '1'.