I'm working on this program, it asked me to compute the sum of all numbers in a string. For example:

Input: There are 10 chairs, 4 desks, and 2 fans.  
Output: 16  
Explanation: 10   4   2 = 16

My program is like this:

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

int main()
{
    string str = "There are 10 chairs, 4 desks, and 2 fans.";
    int sum = 0;

    for(int i = 0; i < str.size(); i  )
    {
        if(str[i] >= 0 && str[i] <= 9)
            sum  = (int)str[i];
    }
    cout << sum << endl;
}

I don't understand why the output of my program is 0, can someone explain what's wrong with my program. Thank you

CodePudding user response：

Alternatively you could use regex, because everyone loves regex.

int main() {
  std::string str = "There are 10 chairs, 4 desks, and 2 fans.";

  std::regex number_regex("(\\d )");

  auto begin = std::sregex_iterator(str.begin(), str.end(), number_regex);
  auto end   = std::sregex_iterator();

  int sum = 0;
  for (auto i = begin; i != end;   i) {
    auto m = *i;
    sum  = std::stoi(m.str());
  }

  std::cout << sum << "\n";
}

CodePudding user response：

You should use ascii code to find the numbers in string. the 0 ascii code is 48 and 9 is 57. after find the number in string you should make whole number for example 10 is 1 and 0. and you should make string with value "10" and use stoi to convert it to int.

  int main()
    {
        string str = "There are 10 chairs, 4 desks, and 2 fans.";
        int sum = 0;
        string number;
        bool new_number = false , is_number ;
        for (int i = 0; i < str.size(); i  )
        {
            // if you use ascii it is good. 
           //but if you use other character encodings.you should use if (str[i] >= '0' && str[i] <= '9')
            if (str[i] >= 48 && str[i] <= 57)
            {
                number  = str[i];
                if (!(str[i 1] >= 48 && str[i 1] <= 57))
                {
                    
                        sum  = stoi(number);
                        number = "";
                }
            }
           
          
        }
        cout << sum << endl;
    }