/in/foo.c: In function 'main':
/in/foo.c:5:1: error: 'a' undeclared (first use in this function)
 a=int(input("请输入一个数"))
 ^
/in/foo.c:5:1: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:3: error: expected expression before 'int'
 a=int(input("请输入一个数"))
   ^~~