/in/foo.c:7:14: error: unknown type name 'node'
 int distance(node a,node b){
              ^~~~
/in/foo.c:7:21: error: unknown type name 'node'
 int distance(node a,node b){
                     ^~~~
/in/foo.c: In function 'main':
/in/foo.c:18:8: warning: implicit declaration of function 'distance' [-Wimplicit-function-declaration]
   sum+=distance(a[i],a[i+1]);
        ^~~~~~~~