checking an int in c++

// CPP program to check if a given string 
// is a valid integer 
#include <iostream> 
using namespace std; 
  
// Returns true if s is a number else false 
bool isNumber(string s) 
{ 
    for (int i = 0; i < s.length(); i++) 
        if (isdigit(s[i]) == false) 
            return false; 
  
    return true; 
} 
  
// Driver code 
int main() 
{ 
    // Saving the input in a string 
    string str = "6790"; 
  
    // Function returns 1 if all elements 
    // are in range '0-9' 
    if (isNumber(str)) 
        cout << "Integer"; 
  
    // Function returns 0 if the input is 
    // not an integer 
    else
        cout << "String"; 
}