foo.c:1:1: warning: data definition has no type or storage class
 a = int(input("请输入一个边长"))
 ^
foo.c:1:1: warning: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
foo.c:1:5: error: expected expression before 'int'
 a = int(input("请输入一个边长"))
     ^~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。