swithc-case question

When I write a simple switch case program:
----------source:

void main()
{
    char e = 0;

    int a=0;
    int b=2;
    int c=3;
    switch(e)
    {
        case 1:
            a = a + b;
            break;
        case 2:
            a = a + c;
            break;
        default:
            break;
    }
}

But,the c51 complier generates:

            ...
     4: void main()
     5: {
     6:     char e = 0;
     7:
C:0x000F    E4       CLR      A
     8:     int a=0;
     9:     int b=2;
    10:     int c=3;
    11:     switch(e)
C:0x0010    24FE     ADD      A,#0xFE
C:0x0012    6002     JZ       C:0016
C:0x0014    04       INC      A
    12:     {
    13:         case 1:
    14:             a = a + b;
    15:             break;
C:0x0015    22       RET
    16:         case 2:
C:0x0016    22       RET
C:0x0017    00       NOP
C:0x0018    00       NOP
C:0x0019    00       NOP
         ...

How could it be possible?