c - array type has incomplete element type adjacency -

i got homework , need write program wich given matrix represents adjacency. user need put matrix in , index , program returns true if there path between 2 values of indexes. example

0 1 2 3 4 1 0 1 0 0 2 0 0 1 0 3 0 0 0 0 4 0 0 0 0 

if user provides matrix (without indexes numbers) , gives value 3,1 returns true because 3 son of 2 , 2 son of one. if user gives value 4,1 returns false.

#include <stdio.h>  #define n 11 #define true 1 #define false 0   int path(long int [][20] a, int u, int v) {     if(u == 0 && a[u][v] == true)         return true;      if(u == 0 && a[u][v] == false)         return false;      if(a[u][v] == false)         return path(a, u--, v);      else if(a[u][v] == true)         return path(a, n, u); }  int main() {     int arr[11][11]  = {{0,1,1,1,0,0,0,0,0,0,0},                         {0,0,0,0,1,1,1,1,1,0,0},                         {0,0,0,0,0,0,0,0,0,1,0},                         {0,0,0,0,0,0,0,0,0,0,1},                         {0,0,0,0,0,0,0,0,0,0,0},                         {0,0,0,0,0,0,0,0,0,0,0},                         {0,0,0,0,0,0,0,0,0,0,0},                         {0,0,0,0,0,0,0,0,0,0,0},                         {0,0,0,0,0,0,0,0,0,0,0},                         {0,0,0,0,0,0,0,0,0,0,0},                         {0,0,0,0,0,0,0,0,0,0,0}};      return path(arr,1,8);     return 0; } 

when try run on gcc returns:

adjacency.c:8:26: error: expected ‘;’, ‘,’ or ‘)’ before ‘a’ adjacency.c: in function ‘main’: adjacency.c:30:1: warning: implicit declaration of function ‘path’ [-wimplicit-function-declaration]

can enybody please tell me why? , if program works?? guys

the function prototypes doesn't match array size.

try changing

int path(long int [][20] a, int u, int v) 

into

int path(long int a[][11], int u, int v)   // move 

and in main change

 int arr[11][11]  

to

 long int arr[11][11]  

or drop long in function

int path(int a[][11], int u, int v) 

btw:

return path(a, n, u); 

is bad n=11. index outside array.

maybe want

return path(a, n-1, u); 

instead avoid indexing array out of range.

important:

return path(a, u--, v); 

probably needs be:

return path(a, --u, v); 

because u-- post-decrement. you'll have endless loop calling path(..) again , again same values.

you want decrement before function call. use --u pre-decrement.