Segmentationfault (linuxc)

Segmentationfault (linuxc) -- Linux general technology-Linux technology and application information. The following is a detailed description. No more than 20 int-type data are read from the keyboard to form an array. The qsort function is used to sort the data and then an integer number is read from the keyboard. The binary method is used for searching.
I have compiled the following functions, but segmentation fault appears during the invisibility.


# Define m 20
# Include
# Include
Int compar (const void * a, const void * B)
{
Int * aa = (int *) a, * bb = (int *) B;
If (* aa> * bb) return 1;
If (* aa = * bb) return 0;
If (* aa <* bb) return-1;
}
Main ()
{
Int base [m], n;
Int I, * key, * itemptr;

Printf ("input n (n <20) \ n ");
Scanf ("% d", & n );
For (I = 0; I {
Scanf ("% d", & base );
}

Qsort (base, n, sizeof (int), compar );
For (I = 0; I {
Printf ("% d", base);
}
Printf ("\ n ");
Scanf ("% d", key );
Itemptr = (int *) bsearch (key, base, 20, sizeof (int), compar );
If (itemptr! = NULL)
{
Printf ("% d is in the table! \ N ", * key );
}
Else
{
Printf ("% d isn' t in the table! \ N ", * key );
}
}

The running result is as follows:

Input n (n <20)
4
1 4 2 3
1 2 3 4
1
Segmentation fault

Thank you for your advice!