Write a C++ program to sum of all positive integers in a sentence

#include <iostream>
using namespace std;
 
int main()
{
    string str1;
    int sum_num = 0, num;
     
    while (getline(cin, str1)) {
        for (int i = 0; i < (int)str1.size(); i++) {
            if (isdigit(str1[i])) continue;
            else {
                str1[i] = ' ';
            }
        }
 
        stringstream abc(str1);
        while (abc >> num) {
            sum_num += num;
        }
    }
    cout << "Sum of all positive integers: " << sum_num << endl;
    return 0;
}