I am trying to write a C User Defined Function. It works in Neatbeans. What I want is, to take value from cells, insert them in text or char array and compare each corresponding array position to each other. As values I will have "1"s and "0s". E.g "101010100011". THe code I wrote in udf.c: /* Comparing bag of words */ char BitAnd(char Cell1[], char Cell2[]) { Cell1[10000]; Cell2[10000]; int counter; float result; int strlen = sizeof(Cell1)/sizeof(Cell1[0])-1; int i; for (i=0; i < strlen; i++) { if (Cell1[i] == Cell2[i]) { counter++; } } result = (float)counter / strlen; } /* MAL wrapper */ char UDFBitAnd(char Cell1[], char Cell2[]) { /* assert calling sanity */ assert(Cell1[] != NULL && Cell2[] != NULL); return MAL_SUCCEED; } In udf.mal I have: command BitAnd(Cell1:chr,Cell2:chr):flt address UDFBitAnd comment "Compare bag of words"; In 80_udf.sql: -- Comparing bag of words create function BitAnd(Cell1[] char, Cell2[] char) returns float external name udf.BitAnd; I compiled Monetdb, but when I try to connect with "monetdb" to db it gives me error. In the log file I found: MSG voc[18857]: !SyntaxException:parseError:command BitAnd(Cell1:chr,Cell2:chr):flt MSG voc[18857]: !SyntaxException:parseError: ^Type identifier expected MSG voc[18857]: !SyntaxException:parseError:command BitAnd(Cell1:chr,Cell2:chr):flt MSG voc[18857]: !SyntaxException:parseError: ^',' expected MSG merovingian[8780]: database 'voc' (18857) has exited with exit status 0 MSG merovingian[8780]: database 'voc' has shut down ERR merovingian[8780]: client error: database 'voc' started up, but failed to open up a communication channel