C++ How can I assign an input value to a std::bitset argument?

Question

I want to make a simple program that will take number of bits from the input and as an output show binary numbers, written on given bits (example: I type 3: it shows 000

Answer 1

A numeric ("non-type", as C++ calls it) template parameter must be a compile-time constant, so you cannot use a user-supplied number. Use a large constant number (e.g. 64) instead. You need another integer that will limit your output:

int x_temp = 10;
cin >> x_temp;
int const bits = 64;
...

Here 64 is some sort of a maximal value you can use, because bitset has a constructor with an unsigned long long argument, which has 64 bits (at least; may be more).

However, if you use int for your intermediate calculations, your code supports a maximum of 14 bits reliably (without overflow). If you want to support more than 14 bits (e.g. 64), use a larger type, like uint32_t or uint64_t.

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A problem with holding more bits than needed is that the additional bits will be displayed. To cut them out, use substr:

cout << bitset<64>(...).to_string().substr(64 - x_temp);

Here to_string converts it to string with 64 characters, and substr cuts the last characters, whose number is x_temp.