I am getting debug error "abort() has been called"

Question

So the problem is that when I run this code compiler ask me to enter value when I enter value and hit enter an error pop saying abort() has been called. Here is my code. how can I remove this error?

#include <iostream>
#include<string>
using namespace std;

class binary
{
private:
    string num;
public:
    void display();
    void chkBin();
};
 void binary::chkBin()
 {
     int x=0;
     for (int i = 0; i <= num.length(); i++)
     {
         if (num.at(i) != '0' && num.at(i) != '1')
         {
             x = -1;
         }
     }
     if (x==-1)
     {
         cout << "The number is not binary";
     }
     else if (x==1)
     {
         cout << "The number is binary";
     }
 }

void binary::display()
{
    cout << "Enter a number"<<endl;
    cin >> num;
}


int main()
{
    binary b;
    b.display();
    b.chkBin();
    return 0;
}

Answer 1

The loop condition i <= num.length() is what makes your program throw std::out_of_range (and then abort). That's because num[num.length()] is out of bounds. You can only access num[0] to num[num.length() - 1] (inclusive) so the loop condition should have been i < num.length().

Also, int x=0; should probably be int x=1; for it to be able to print The number is binary.

When you want to go through the whole range, you can (since C++11) use a range-based for loop instead which makes it easier to avoid mistakes like this.

Example:

void binary::chkBin()
{
    for (auto ch : num)                   // a range-based for loop
    {
        if (ch != '0' && ch != '1')
        {
            std::cout << "The number is not binary\n";
            return;
        }
    }
    std::cout << "The number is binary\n";
}