Why does this code cause an out_of_range error?

Question

https://code.sololearn.com/csGBIZ4Qy7gs/#cpp

If you enter a range above 65535, the substr()-function will cause an out_of_range error.
66535 is the maximum value of a uint16_t, so my guess is that somewhere, either in the string or in the substr()-function, this datatype is being used.

Can anyone explain? Thanks in advance!

Answer 1

Replacing function args type and variable square type with long long int appears to fix the issue. I believe 66535 caused an overflow which happens to mess with either stringstream or/then substr.

And yes. Further inspection says that your code here:

string compare = square_str.substr(square_str.length()-number_str.length(), number_str.length());

assumes that square_str.length() will always be larger than number_str.length(), which is untrue for cases of overflow.

Answer 2

Oh, of course! Overflow makes perfect sense, as the square of 2^16 (= 2^32) is outside the range of int.
Thank you very much!