[c++] How do I select a range of values in a switch statement?

When I try to compile I get this error:

1>------ Build started: Project: snake, Configuration: Debug Win32 ------
1>  exercise.cpp
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(13): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(16): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(19): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(22): error C2059: syntax error : '>='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(25): error C2059: syntax error : '>'
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(28): error C2059: syntax error : '=='
1>c:\users\robin\documents\visual studio 2010\projects\snake\snake\exercise.cpp(34): warning C4065: switch statement contains 'default' but no 'case' labels
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Code:

#include <iostream>
using namespace std;

int main(){
    int score;

    //Vraag de score
    cout << "Score:";
    cin >> score;

    //Switch
    switch(score){
        case >= 100:
            cout << "a";
            break;
        case >= 50:
            cout << "b";
            break;
        case >= 25:
            cout << "c";
            break;
        case >= 10:
            cout << "d";
            break;
        case > 0:
            cout << "e";
            break;
        case == 0:
            cout << "f";
            break;
        default:
            cout << "BAD VALUE";
            break;
    }
    cout << endl;
    return 0;
}

How can I fix this problem? It's a console application, Win32 and my IDE is Windows Enterprise C++ 2010.

I'm learning from Beginning C++ Through Game Programming.