Help

[hqzkaoyan]

Hello,
I am a student from China and my study on CS has several years. My name is 
Qizhi Hu. Recently, when I use bison, there are some problems I can't 
understand. For example:
a:b is a rule and both are pointer of int. when parsing, the following will not 
work.
a:b
{
    assert($$==NULL);
}
;
But, when the rule become a: b c or a: b c d, all symbols are type of int* 
,then following will work well.
a: b c
{
    assert($$==NULL);
}
;
Can you help me ?
 Best,
Qizhi Hu

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