Usage of exit()

I've found this code and I don't understand why they end the program with exit(0) when the input is not valid. Why they didn't use exit(1)? I've heard that we should use exit(1) when there is a failure. So when I should use EXIT_FAILURE or EXIT_SUCCESS?

#include<iostream>
using namespace std;
int main()
{
    int i;
    cout<<"Enter a non-zero value: ";  //user input
    cin>>i;
    if(i)    // checks whether the user input is non-zero or not
    {
        cout<<"Valid input.\n";
    }
    else
    {
        cout<<"ERROR!";  //the program exists if the value is 0
        exit(0);
    }
    cout<<"The input was : "<<i;
}