系统内存不足吗？(Is the system memory-less?)

 移位并添加： 
 
exModel = 0x2;
model = 0xE;

output = (exModel << 4) + model;
 
 由于在上面的评论中提到过，你也可以使用联合，但我不会推荐它 - 它使代码非常不便携（并且我认为违反了严格的别名规则）： 
 
union myUnion
{
    unsigned char output;
    struct
    {
        unsigned char model   : 4; // the order of these two fields
        unsigned char exModel : 4; // is system dependent
    };
};

union myUnion u;

u.exModel = 0x2;
u.model = 0xE;

output = u.output;

Shift and add:
 
exModel = 0x2;
model = 0xE;

output = (exModel << 4) + model;
 
Since it was mentioned in the comment above, you could also use a union, but I wouldn't recommend it - it makes the code pretty nonportable (and I think violates strict aliasing rules):
 
union myUnion
{
    unsigned char output;
    struct
    {
        unsigned char model   : 4; // the order of these two fields
        unsigned char exModel : 4; // is system dependent
    };
};

union myUnion u;

u.exModel = 0x2;
u.model = 0xE;

output = u.output;