Convert each digit from number saved in string to array of int

Question

I'm writing this project on DFA and i want to save and covert each digit of an integer saved as a string to an int array.This is the code from the function responsible for that:

---

int l=final_states.size();
int* temp_final;
temp_final=new int [l];
for(int i=0;i<l;i++)
{
    temp_final[i]=atoi(final_states.at(i).c_str());
}

---

This gives me the following mistake : request for member 'c_str' in '((DFA*)this)->DFA::final_states.std::basic_string<_CharT, _Traits, _Alloc>::at<char, std::char_traits<char>, std::allocator<char> >(((std::basic_string<char>::size_type)i))', which is of non-class type 'char'|.

---

So if you could tell me how to make this conversion and saving work , that would be great.

Answer 1

The atoi() function wants a const char*, you cannot call .c_str() with the result of .at(i) which is actually a char& value.

Just fix your assignment line to

 temp_final[i] = int(final_states[i]) - int('0');

Though you also might check if you really have a digit there, before putting it into your result array:

 if(std::isdigit(final_states[i])) {
     temp_final[i] = int(final_states[i]) - int('0');
 }
 else {
     // Skip, or throw error ...
 }

Answer 2

c_str() doest not work because after calling at(i) you've got a char not a string. I suggest you to use:

temp_final[i]=final_states.at(i) - '0';

Here you take an ASCII code for a char symbol and when you subtract a '0' you get exectly an int you need, because all the digits go in order in ASCII table.