Problem converting a std::string of digits to vector

Question

I am supposed to get two big integer numbers (up to 600 digits) from console screen and write the result on the console again.

I defined two variables of type std::string to store two big integer numbers .I take their values from the user. To take the sum of that two numbers, I defined two vectors to store the digits of that two strings of numbers .

Here is the problem, when I try to loop through the vector to print the digits that I took from strings of numbers I get the following result .The Ascii values of the digits are printed on The Console. Could anyone tell me how to fix this problem please.

Note: The code is still not complete .

For the first string I took the numbers 9 8 7 6 5 4 3 2 1 from the user , on the console window I got the following result.

[0]57

[1]56

[2]55

[3]54

[4]53

[5]52

[6]51

[7]50

[8]49

    #include <iostream>
    #include <sstream>
    #include <vector>
    #include <algorithm>


    std::string Sum_Of_Two_Long_Integers()
    {
      std::string First_String ;
      std::string Second_String ;
      std::string Result_String ;

      std::cout << "Please enter the first number: " ;
      std::getline(std::cin, First_String);
      std::cout << "Please enter the second number: " ;
      std::getline(std::cin, Second_String);

      std::vector <int> First_String_Vector (First_String.length()) ;
      std::vector <int> Second_String_Vector (Second_String.length()) ;

      for(int Counter = 0 ; Counter  < First_String_Vector.size() ; ++ Counter)
      {
         First_String_Vector[Counter] = First_String[Counter] ;
         Second_String_Vector[Counter] = Second_String[Counter] ;
         std::cout << "[" << Counter << "]" << First_String_Vector[Counter] << std::endl ;
      }

      return Result_String ;
   }

   int main()
   {
      std::string Result_String  = Sum_Of_Two_Long_Integers() ;
      std::cout << "Result = " << Result_String << std::endl ;

      return 0 ;
   }

Answer 1

First_String_Vector[Counter] = First_String[Counter] ;
Second_String_Vector[Counter] = Second_String[Counter] ;

The digits are stored as ASCII in you string, you should convert to integer before placing them into the vector.

This would do the trick:

First_String_Vector[Counter] = First_String[Counter] - '0';
Second_String_Vector[Counter] = Second_String[Counter] - '0';

I would also add a check for valid input before populating your vectors to make sure that you only read digits:

if(First_String[Counter] < '0' || First_String[Counter] > '9' ||
   Second_String[Counter] < '0' || Second_String[Counter] > '9')
{
    std::cout << "Invalid input\n";
    return "":// Or better throw an exception
}

EDIT: '6' isn't equal to 6. The first one is a char, its value is ASCII for character '6', and the second is the integer 6.

ASCII is an encoding. Characters are mapped to some numbers. Value for '0' is 48, '1' is 49, ..., '9' is 57

To be even more precise C++ does not guarantee to use ASCII encoding (though I don't know of an implementation that does not use it), but it does guarantee that '0'...'9' have contiguous integer values. So '6' - '0' will give us integer 6.