Why the do\while loop is breaking and Terminal is hanged? - c++

Question

I have the following code and it somehow verify if the input is number, but the error occurs while looping back to ask the user for the second time to enter the number.
I can't figure it out.
#include <iostream>
#include <limits>
using namespace std;
void botVarification();
void userDecision();
bool isHuman(string humanInput);
int main()
{
botVarification();
return 0;
}
void botVarification()
{
string humanInput;
cout << "Enter the number to verify that you are not a bot: ";
cin >> humanInput;
bool isHuman = true;
do {
for (int humanInputvalidator; humanInputvalidator < humanInput.length() && isHuman; humanInputvalidator++) {
if (!(humanInput[humanInputvalidator] >= 48 && humanInput[humanInputvalidator] <= 57)) {
isHuman = false;
cout << "Not success, try again!";
cin >> humanInput;
}
else
cout << "Success" << '\n';
break;
}
} while (!(isHuman));
}

Answer 1

$ clang++-7 -Wall -o main main.cpp
main.cpp:23:39: warning: variable 'humanInputvalidator' is
uninitialized when used here [-Wuninitialized]
for (int humanInputvalidator; humanInputvalidator < hum...
^~~~~~~~~~~~~~~~~~~
main.cpp:23:37: note: initialize the variable 'humanInputvalidator' to
silence this warning
for (int humanInputvalidator; humanInputvalidator < hum...
^
= 0
1 warning generated.
So let's fix that.
Additionally, on the second iteration of getting input from the user, humanInputvalidator < humanInput.length() && isHuman will always be false. You'll want to reinitialize isHuman = true inside the do while loop.
Functions are a great way to simplify your code!
Use functions! It's a great way to simplify your code and decrease the number of variables in any single context.
bool isThisHumanInput(std::string data) {
for (int i = 0; i < data.length(); i++)
if (!(data[i] >= 48 && data[i] <= 57))
return false;
return true;
}
void botVarification()
{
string humanInput;
bool isHuman;
do {
cout << "Enter the number to verify that you are not a bot: ";
cin >> humanInput;
isHuman = isThisHumanInput(humanInput);
if (isHuman) {
cout << "Success" << '\n';
} else {
cout << "Not success, try again!\n";
}
} while (!isHuman);
}

Answer 2

There's several changes that are necessary to get this code functioning correctly. Here's one working version, with the functions and includes that you don't actually use yet removed and a typo corrected.
Highlights: We have to initialize humanInputvalidator, we have to reset isHuman to true at the beginning of the do-while loop, and the logic for exiting the inner for loop and printing "Success!" was all changed.
#include <iostream>
#include <string>
void botVerification();
int main()
{
botVerification();
return 0;
}
void botVerification()
{
std::string humanInput;
std::cout << "Enter the number to verify that you are not a bot: ";
std::getline(std::cin, humanInput); // getline to capture whitespace
bool isHuman;
do {
isHuman = true; // Reset to true at the beginning of each loop
// Initialize humanInputvalidator
for (int humanInputvalidator = 0; humanInputvalidator < humanInput.length() && isHuman; humanInputvalidator++) {
// Rewrite comparison using char literals for clarity
if (!(humanInput[humanInputvalidator] >= '0' && humanInput[humanInputvalidator] <= '9')) {
isHuman = false;
std::cout << "Not success, try again! ";
std::getline(std::cin, humanInput);
// No need to break since we test isHuman in the for loop
}
}
} while (!(isHuman));
// Print success after input is fully verified, not at some intermediate stage
std::cout << "Success!\n";
}

Answer 3

First of all, you need to initialize humanInputvalidator when you define it in the for loop. Variables in C++ do not have default values.
Also, in case you find an incorrect character in humanInput, you make the user input again. This happens while you are iterating over the characters in the string. This is not really good. In this particular case it does not break, but it may in some other one, so keep that in mind.
Moreover, in the for loop you alway break on the first iteration. Your break statement is just below the if-else and I think your intention was that it be inside the else branch.
All in all, I cannot pinpoint any specific reason for the infinite loop you are getting but these are at least a few things you can fix and then see what happens. I would also suggest to simplify your code and make it more readable, by splitting out the invalid input check to a separate function, like this:
bool isInputValid(const string& humanInput)
{
for (int humanInputvalidator = 0; humanInputvalidator < humanInput.length(); humanInputvalidator++) {
if (!(humanInput[humanInputvalidator] >= 48 && humanInput[humanInputvalidator] <= 57)) {
return false;
}
}
return true;
}
void botVarification()
{
string humanInput;
cout << "Enter the number to verify that you are not a bot: ";
cin >> humanInput;
do {
if (isInputValid(humanInput))
{
cout << "Success" << '\n';
break;
}
cout << "Not success, try again!";
cin >> humanInput;
} while (true);
}