/in/foo.c: In function 'main':
/in/foo.c:5:6: error: 'a' undeclared (first use in this function)
      a=int(input("小朋友人数:"))
      ^
/in/foo.c:5:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:8: error: expected expression before 'int'
      a=int(input("小朋友人数:"))
        ^~~
/in/foo.c:18:1: error: expected declaration or statement at end of input
 }
 ^