c++ - why is this not returning true (loop-logic) -

c++ - why is this not returning true (loop-logic) -

std::string turnsdefined; std::cin >> turnsdefined; bool haspassed; while(haspassed != true){ for(char c : turnsdefined){ if(isdigit(c) != true){ std::cout << "please utilize numbers describe amount of turns you'd do." << std::endl; haspassed = false; break; std::cin >> turnsdefined; }else{ haspassed = true; } } }

i've stumbled upon this. shortened downwards code (by reasonable amount) can seek yourself.

this short programme should check if come in contains (unwanted) letters. thing don't understand: way wrote it, pretty sure if typed test2test it's gonna pass (even though contains letters) because if statement recognize 1 single number , set haspassed true.

i hope create sense of wrote. happy reply farther questions.

bool haspassed not initialized in code. should declare as:

bool haspassed = false;

live code here

uninitialized automatic (local , non static) variables contain in-determinant value. reading them prior assigning value results in undefined behavior. (compiler free blunder here in practice may contain true or false or other non-sense value)

editfrom andy newman's comment: status if(isdigit(c) != true) suspectible. because isdigit returns int should avoid comparing true.

isdigit returns non-zero value (true) if character numeric character, 0 (false) otherwise.

you can improve rewrite status as:

if(isdigit(c)) {

even if function returns bool, superfluous compare true or false

c++ loops logic