c++ : check if it is a Number in class

Question

in this code I want to know if two numbers are Int Or String :

#include <iostream>
using namespace std;

class calculate{
    private:
        bool checkNumbers(int num1, int num2){
            if(isdigit(num1) && isdigit(num2)){
                return true;
            }else{
                return false;
            }
        }

public:
    void sum(int x, int y){
        bool chek=checkNumbers(x, y);
        if(chek==true){
            cout<< "yes it is Number"<< endl;
        }else{
            cout<< "Nope! String"<<endl;
        }
    }
};

int main()
{
    calculate calulate;
    calulate.sum(3, 2);
    return 0;
}

But after run code, I just see Nope! String , it mean it is string. who know what is wrong? I checked numbers with isdigit and I just sent two numbers

calulate.sum(3, 2);

but nothing!! thanks

Answer 1

Your issue is with your usage of std::isdigit(int)

The function is meant to check if a int is equivalent to one of the 10 char -represented decimal digits, 0123456789 . However, this function is only true for int values of 48-57.

int is expected to be the integer value of a char . If you want it to resolve true , use 48-57, where 48 is 0 , 49 is 1 , etc...

Note that your function would naturally resolve to true if you passed it a char such as '3', like one commenter stated. This is because char(3) == int(51) .

eg:

isdigit('1'); // This is true, because '1' is a "char" digit
isdigit(49); // This is true

isdigit(1); // This is false
isdigit(60); // This is false

Answer 2

num1 and num2 are interpreted as characters by std::isdigit . Typically this means ASCII characters .

And as an ASCII character 2 and 3 are control characters and not digits, which are in the range of '0' (0x30) to '9' (0x39)