making an if statement that will check the variable's type

Question

I'm a c++ beginner . and im trying to build a program that will check if my float variable is float . then continue the program . but if not you will have to try again . thats what ive done for the moment .

    while (true)
{
    cout << "Okay, pick a  number: " << flush;
    cin >> num1;

    

}

idk how to build an if statement with my needings and need help from you guys.

im trying to make a calculator , by far my code is

    float num1;
char continueQuestion;
float num2;
char op;

cout << "______________________________________________________" << endl;
cout << "                                                      " << endl;
cout << "          Welcome to the amazing calculator!          " << endl;
cout << "______________________________________________________" << endl;


while (true)
{
    cout << "Would you like to continue? <y/n>: " << flush;
    cin >> continueQuestion;

    if (continueQuestion == 'y') {
        break;
    }
    else if (continueQuestion == 'n')
    {
        exit(0);
    }
    else
    {
        cout << "That is not an answer!" << endl;
    }
    
}


while (true)
{
    cout << "Okay, pick a first number: " << flush;
    cin >> num1;

    

}

and if you dont got it im trying to reach for an if statement that will check if my var num1 is not a float so print something . and i cant do that so i request help from you.

Before posting their first question on stackoverflow.com, everyone should take the [tour], read the [help], understand all the requirements for a [mre] and [ask] questions here. Not doing any of this results in a poor quality question; which gets downvoted, closed, and then deleted. — Sam Varshavchik, Nov 21 '20 at 15:45
A `float` is always a `float`. Do you want to validate/parse input instead? For that, use these three words plus your programming language as search terms. As a new user here, also take the [tour] and read [ask]. — Ulrich Eckhardt, Nov 21 '20 at 15:45
do you consider an input `3` as invalid, because it has no fractional part? Or do you only want to catch wrong input that is not a number, like `ABC` ? — 463035818_is_not_an_ai, Nov 21 '20 at 15:51

score 0 · Answer 1 · answered Nov 21 '20 at 15:46

0

You can check with that way;

(int)x = num1 

int(x) == x // if num1 is not float  returns true

---------

(int)x = num1

int(x) == // if number is float x returns false

answered Nov 21 '20 at 15:46

Yusuf Şengün

284
3
13

the variable is a float and not an int. would it be different if i'll change it? – virtual Nov 21 '20 at 15:48

score 0 · Answer 2 · answered Nov 21 '20 at 15:54

This code uses a helper function from the following answer.

#include <string>
#include <sstream>
#include <iostream>

bool isFloat(std::string myString) {
    std::istringstream iss(myString);
    float f;
    iss >> std::noskipws >> f; // noskipws considers leading whitespace invalid
    // Check the entire string was consumed and if either failbit or badbit is set
    return iss.eof() && !iss.fail(); 
}

int main() {
    float num1;

    while (true) {
        std::string input;

        std::cout << "Okay, pick a number: " << std::flush;
        std::cin >> input;

        if (isFloat(input)) {
            num1 = std::stof(input);
            break;
        }
    }
}

if this question is a duplicate of another question we should close it as duplicate instead of repeating an answer that already exists elsewhere — 463035818_is_not_an_ai, Nov 21 '20 at 16:22
@idclev463035818 I don't think it's considered a duplicate, but feel free to check and reply back. — XDarkDev, Nov 21 '20 at 16:28

making an if statement that will check the variable's type

2 Answers2