/in/foo.c:1:1: warning: data definition has no type or storage class
 s=input("字符串")
 ^
/in/foo.c:1:1: warning: type defaults to 'int' in declaration of 's' [-Wimplicit-int]
/in/foo.c:1:3: warning: implicit declaration of function 'input' [-Wimplicit-function-declaration]
 s=input("字符串")
   ^~~~~
/in/foo.c:1:3: error: initializer element is not constant
/in/foo.c:2:1: error: expected ',' or ';' before 'a'
 a=s(::-1)
 ^