Optimizing simple C++ grading program I have started working on the projects listed here.  I want to practice my C++ coding skills.  I would love any constructive criticism I can get!

This is for the very first problem, #1 "Grading Program"

#include &lt;iostream&gt;
using std::cout;
using std::cin;

int main()
{
    int UserNumber;
    char Grade;

    cout &lt;&lt; "Enter the grade you got on that test: ";
    cin &gt;&gt; UserNumber;
    cout &lt;&lt; "\n\n\n";

    if (UserNumber &gt; 89 &amp;&amp; UserNumber &lt; 101)
    {
        Grade = 'A';
    }

    else if (UserNumber &gt; 79 &amp;&amp; UserNumber &lt; 91)
    {
        Grade = 'B';
    }

    else if (UserNumber &gt; 69 &amp;&amp; UserNumber &lt; 81)
    {
        Grade = 'C';
    }

    else if (UserNumber &gt; 59 &amp;&amp; UserNumber &lt; 71)
    {
        Grade = 'D';
    }

    else if (UserNumber &gt; -1 &amp;&amp; UserNumber &lt; 61)
    {
        Grade = 'F';
    }
    else
    {
        Grade = 'Z';
    }


    switch (Grade)
    {
    case 'A':
        cout &lt;&lt; "Perfect! You got a: " &lt;&lt; Grade;
        break;
    case 'B':
        cout &lt;&lt; "Could've been worse. You got a: " &lt;&lt; Grade;
        break;
    case 'C':
        cout &lt;&lt; "It's okay I guess, you got a: " &lt;&lt; Grade;
        break;
    case 'D':
        cout &lt;&lt; "Uggh.. You got a: " &lt;&lt; Grade;
        break;
    case 'F':
        cout &lt;&lt; "Better luck next time! You got a: " &lt;&lt; Grade;
        break;
    case 'Z':
        cout &lt;&lt; "Undefined value! Make sure it's a value from 0-100!";
        break;


    }
    cout &lt;&lt; "\n\n\n\t\t\t";
    return 0;
}
There's probably much that can be done, but I'll give it a quick review:


Are only integer grades allowed?  They can be decimals in real life, and that would make for a more robust grading system.
Consider renaming UserNumber to something like numericalGrade.  The former sounds like it's for an ID number, not a grade.
Do not "list" variables at the top of a function in C++, unless it's absolutely necessary.  Here, you can declare UserNumber between the std::cout and std::cin.
There's no need for a Z case here.  Use a default case instead, which will be reached if no other case is reached.
You don't need an explicit return 0 at the end.  The compiler will do this return for you at the end of main() as successful termination is always implied here.