Question

I’ve written this code to extract numbers from a string using a string iterator.
The iterator picks up the first number and decides to call it a day.
Why’s it so?

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

int main()
{
 string myAge = "I am 23 years old";
 string::iterator iterator;
 char numberInCharacterForm;
 string numberInStringForm;
 stringstream convertToString;
 for(iterator = myAge.begin();iterator!=myAge.end();iterator++)
 {
              numberInCharacterForm = *iterator;
              if(numberInCharacterForm >= '0' & numberInCharacterForm <='9')
              {
               convertToString << numberInCharacterForm;
               convertToString >> numberInStringForm;
              }
 } 
 cout << numberInStringForm <<endl;   
 getch();
 return 0;
}

Output is 2;

Answer 1

Just collect the characters into the stringstream and print it afterwards:

for(iterator = myAge.begin();iterator!=myAge.end();iterator++)
{
    numberInCharacterForm = *iterator;
    if(numberInCharacterForm >= '0' && numberInCharacterForm <='9') {
       // note: && instead of & here ^
       convertToString << numberInCharacterForm;
    }
 }   
 cout << convertToString.str() <<endl;   

However there is no need for manual iteration over the string:

string myAge = "I am 23 years old"; 
string numberInStringForm;
std::remove_copy_if(myAge.begin(), myAge.end(), 
                    std::back_inserter(numberInStringForm),
                    std::not1(std::ptr_fun(isdigit)));
std::cout << numberInStringForm << std::endl;