How to check if input is numeric in C++?

Here we will see how to check whether a given input is numeric string or a normal string. The numeric string will hold all characters that are in range 0 – 9. The solution is very simple, we will simply go through each characters one by one, and check whether it is numeric or not. If it is numeric, then point to the next, otherwise return false value.

Example

#include <iostream>
using namespace std;
bool isNumeric(string str) {
   for (int i = 0; i < str.length(); i++)
      if (isdigit(str[i]) == false)
         return false; //when one non numeric value is found, return false
      return true;
}
int main() {
   string str;
   cout << "Enter a string: ";
   cin >> str;
   if (isNumeric(str))
      cout << "This is a Number" << endl;
   else
      cout << "This is not a number";
}

Output

Enter a string: 5687
This is a Number

Output

Enter a string: 584asS
This is not a number