prepare (1/3): 
finished

make (2/3): 
gcc -g -Wall -o main prim.c
prim.c: In function 'main':
prim.c:57:13: error: 'g' undeclared (first use in this function)
     int low[g->v_num];
             ^
prim.c:57:13: note: each undeclared identifier is reported only once for each function it appears in
prim.c:58:9: warning: unused variable 'mst' [-Wunused-variable]
     int mst[g->v_num];
         ^~~
prim.c:57:9: warning: unused variable 'low' [-Wunused-variable]
     int low[g->v_num];
         ^~~
Makefile:2: recipe for target 'all' failed
make: *** [all] Error 1

build failed