How to check if input is an integer using C/C++?

Here we will see how to check if the given input is an integer string or a normal string. The integer string will contain all characters in the range 0-9. The solution is very simple, we will check each character one by one and then check if it is a number. If it is a number, it points to the next character, otherwise it returns a 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

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