C++ Program:

Example:

#include <iostream>
using namespace std;

int main() {
  int n1;
  cout<<"Enter your number: ";
  cin>>n1;
  if(n1%2==0) cout<<"Even Number";
  else cout<<"Odd number";
  return 0;
}

Output:

  Enter your number : 4
  Even Number

You should know first :

Even numbers: Numbers perfectly divisible by 2

(number % 2 == 0)

Odd numbers: Numbers not perfectly divisible by 2

(number % 2 != 0)

you can use any one of the above as condition and in else portion just print the other one