Question

In C++, better without Boost library, how to make sure that the std::string str contains either a number or a number followed by ‘%’ sign? If it does not belong to these two cases an error should be issued.

Answer 1

#include <iostream>
#include <string>
#include <algorithm>
#include <ctype.h>
bool is_a_bad_char(char c) {
  return !(isdigit(c) || (c=='%'));
}

int main() {
  std::string str = "123123%4141219";
  if (std::find_if(str.begin(), str.end(), is_a_bad_char) != str.end()) {
    std::cout << "error" << std::endl;
    return 1;
  }
  return 0;
}