C++ efficient method of formatting std::cout

How would one more cleanly format this while keeping spaces?

I wouldn't print out any hard-coded space characters at all. I would let std::cout pad out the values as needed, via the std::setw and std::setfill stream manipulators, eg:

#include <iostream> #include <iomanip> int main() { std::cout << "Calculator App" << std::endl; double num1, num2; std::cin >> num1; std::cin >> num2; std::cout << std::setfill(' '); std::cout << std::left << std::setw(15) << "First number:" << num1 << std::endl; std::cout << std::left << std::setw(15) << "Second number:" << num2; << std::endl; return 0; }

Output:

Calculator App First number: 5.3 Second number: 81.1

Online Demo

Since "First number:" and "Second number:" are less than 15 characters in length, the fill character ' ' will be output automatically, eg:

+---------------------- 15 width ---------------------------+ | | +---------------------------------------------------------------------------+ | F | i | r | s | t | | n | u | m | b | e | r | : | | | 5 | . | 3 | ⏎ | +---------------------------------------------------------------------------+ ^ ^ fill chars +---------------------- 15 width ---------------------------+ | | +-------------------------------------------------------------------------------+ | S | e | c | o | n | d | | n | u | m | b | e | r | : | | 8 | 1 | . | 1 | ⏎ | +-------------------------------------------------------------------------------+ ^ fill char

Switch to a version of C++ that supports std::print or use C++20's std::format.

Which will provide much cleaner and readable syntax (std::print might even be a bit more efficient at runtime)

And finally if you want to learn C++, don't do it by online judge/competitive coding.
Find a good book, visit https://learncpp.com/. And you might want to have a look at the
C++ core guidelines.
So you can at least compare your training material against how C++ actually should be used
(most training material just is outdated).

#include <iostream> #include <format> #include <print> int main() { std::cout << "Calculator App\n"; double num1, num2; std::cin >> num1; std::cin >> num2; // C++20 std::cout << std::format("{:<15}{}\n", "First number:", num1); std::cout << std::format("{:<15}{}\n", "Second number:", num2); // C++23 std::print("{:<15}{}\n", "First number:", num1); std::print("{:<15}{}\n", "Second number:", num2); return 0; }

It's hard to guess whether it applies in this specific case, but when you need specific formatting in general, it can be useful to wrap the data up into a class, and overload operator<< for that class to assure consistent formatting. But we also want it to be easy to use, so in this case, we may want a user defined literal operator to keep things neat and tidy, so to speak:

#include <iostream> #include <iomanip> #include <string_view> class Label { std::string_view label; public: Label(char const *s, std::size_t len) : label(s, len) {} friend std::ostream &operator<<(std::ostream &os, Label l) { return os << std::left << std::setw(15) << l.label; } }; Label operator""_L(char const *s, std::size_t len) { return Label(s, len); } int main() { double num1, num2; std::cin >> num1; std::cin >> num2; std::cout << "Calculator App\n"; std::cout << "first number:"_L << num1 << '\n'; std::cout << "second number:"_L << num2 << '\n'; }

The operator""_L allows use to use _L as a suffix on a string literal to create a Label object, which overloads operator<< to use the formatting we want, so our result will come out like we want:

1.234 3.456 first number: 1.234 second number: 3.456

For a real calculator app, we might (easily) want to use a class with overloaded operator<< for each operand as well, so we print the numbers out consistently formatted as well (but in this case, we probably don't need/want the user defined literal operator).