/in/foo.c: In function 'main':
/in/foo.c:6:6: error: 'i' undeclared (first use in this function)
  for(i=0;i<a;i++){
      ^
/in/foo.c:6:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:9:9: error: expected ';' before ':' token
  for(i=0:i<a;i++){
         ^
/in/foo.c:9:17: error: expected ';' before ')' token
  for(i=0:i<a;i++){
                 ^
/in/foo.c:15:1: error: expected ';' before 'return'
 return 0;
 ^~~~~~
/in/foo.c:5:6: warning: variable 'b' set but not used [-Wunused-but-set-variable]
  int b[a];
      ^