/in/foo.c:5:7: error: 'N' undeclared here (not in a function)
 int a[N];  
       ^
/in/foo.c: In function 'main':
/in/foo.c:46:9: warning: implicit declaration of function 'mem' [-Wimplicit-function-declaration]
         mem(a,0);  
         ^~~
/in/foo.c:60:5: error: expected declaration or statement at end of input
     return 0;
     ^~~~~~
/in/foo.c:43:15: warning: unused variable 'z' [-Wunused-variable]
     int x, y, z;  
               ^
/in/foo.c:43:12: warning: unused variable 'y' [-Wunused-variable]
     int x, y, z;  
            ^
/in/foo.c:43:9: warning: unused variable 'x' [-Wunused-variable]
     int x, y, z;  
         ^
/in/foo.c:42:15: warning: unused variable 'k' [-Wunused-variable]
     int i, j, k;  
               ^
/in/foo.c:42:12: warning: unused variable 'j' [-Wunused-variable]
     int i, j, k;  
            ^