While input is a letter this works fine but if I input a float number, for example 5.5 it stops. The question is how can I check if a float or double is entered?

int main(){
 
  int a;

  cout<<"enter a number:"<< endl;

  while(!(cin>>a)) {
       cin.clear();
   
       cin.ignore(256,'\n');
   
       cout << "wrong input\n";
  }
}

CodePudding user response：

You might try something like this:

#include <iostream>
#include <cmath>
int main()
{
    double in;
    double ceil_in;
    double diff;

    do {
        while (!(std::cin >> in))
        {
            std::cin.clear();
            std::cin.ignore(123, '\n');
        }
        ceil_in = ceil(in);
        diff = in - ceil_in;
    } while(diff != 0.0);
    std::cout << "Finish." << std::endl;
    return 0;
}

Now it should work with strings too. Let me know if it addresses your problem.

CodePudding user response：

Just read whole line then try read integer from it checking if everything was read.

bool scan_int(const std::string& s, int& x) {
    std::istringstream in{s};
    return in >> x >> std::ws && in.eof();
}

int main()
{
    std::string s;

    while(std::getline(std::cin, s)) {
        int x;
        if (scan_int(s, x)) {
            std::cout << "Integer found: " << x << '\n';
        } else {
            std::cout << '"' << s << "\" is not an integer\n";
        }
    }

    return 0;
}

https://godbolt.org/z/xdcjzrEEd

CodePudding user response：

Two questions in one!

1. How do I repeat some code multiple times?
2. How do I read an integer from standard input?

This answer attempts to separate those 2 questions and also to show an extendable approach, just in case your next homework assignment will be to read not an int but a float or a hex number or 5 integers or whatever... and maybe from a file and not standard input...

For question 1, see main() in the code below, for question 2, see read_fixnum().

#include <iostream>
#include <regex>
#include <string>

bool read_fixnum(std::istream& is,
         std::string prompt,
         int& result) {
  std::regex fixnum{"\\s*(\\d )\\s*"};
  std::cout << prompt << std::endl;
  std::string line;
  if (std::getline(is,line)) {
    std::smatch match_result;
    if (std::regex_match(line, match_result, fixnum)) {
      result = std::stoi(match_result.str());
      return true;
    }
  }
  return false;
}


int main(int argc, const char* argv[]) {

  int number = 0;
  bool running = true;
  while (running) {
    if (read_fixnum(std::cin,
            "enter an integral number: ",
            number)) {
      running = false;
    }
  }

  std::cout << "you entered: " << number << std::endl;
  
  return 0;
}