Question

I have a int var; and using cin, but how to check if user input a float or give me a solution for this problem?

Answer 1

There is no easy way of doing this. Input via the >> operator is really not intended for interaction with humans who may enter the wrong thing. You will have to read the input as a string and then check it using a function like strtol, or your own hand-rolled code.

Here’s an outline of an approach using strtol:

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

bool GetInt( istream & is, int & n ) {
    string line;
    if ( ! getline( is, line ) ) {
        return false;
    }
    char * ep;
    n = strtol( line.c_str(), & ep, 10 );
    return * ep == 0;
}


int main() {
    int n;

    while(1) {
        cout << "enter an int: ";
        if ( GetInt( cin, n ) ) {
            cout << "integer" << endl;
        }
        else {
            cout << "not an integer" << endl;
        }
    }
}